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BLAIR FUNDS00008226322013-05-012013-05-01false2012-12-31<b>FEES AND EXPENSES:</b>00.0326<b>Example: </b>95018194064<b>Portfolio Turnover: </b><b>Example: </b>3716501446<b>Portfolio Turnover: </b><b>Example: </b>4427701696<b>Portfolio Turnover: </b>The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of mid cap domestic growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. The securities of mid cap companies may be more volatile and less liquid than securities of large cap companies. In addition, mid cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance. The Fund is designed for long-term investors.<b>Example:</b>85415933547<b>Portfolio Turnover:</b>77514623297<b>Portfolio Turnover: </b>The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of mid cap domestic value companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., value vs. growth, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. The securities of mid cap companies may be more volatile and less liquid than the securities of large capitalized companies. In addition, mid cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance. The Fund is designed for long-term investors.<b>Example:</b>143927005709<b>Portfolio Turnover:</b>4187301615<b>Example:</b>522<b>Example: </b><b>Portfolio Turnover: </b><b>Example: </b>132825175400<b>Portfolio Turnover: </b>4958611892<b>Example: </b>243434987<b>Portfolio Turnover: </b><b>Annual Total Returns.</b><b>Example: </b>5139041998<b>Portfolio Turnover: </b><b>Example: </b>2654601025<b>Portfolio Turnover: </b><b>Example: </b>4057041553<b>Portfolio Turnover: </b><b>INVESTMENT OBJECTIVE: </b><b>FEES AND EXPENSES:</b><b>Example: </b>3656331398<b>Portfolio Turnover: </b><b>INVESTMENT OBJECTIVE: </b><b>FEES AND EXPENSES:</b><b>Example: </b><b>Portfolio Turnover: </b>4567871724<b>FEES AND EXPENSES: </b><b>Example: </b>5269292057<b>Portfolio Turnover: </b><b>INVESTMENT OBJECTIVE: </b><b>FEES AND EXPENSES: </b><b>Example: </b>5088761911<b>Portfolio Turnover: </b><b>INVESTMENT OBJECTIVE: </b><b>FEES AND EXPENSES: </b><b>Example: </b>5339181998<b>Portfolio Turnover: </b><b>INVESTMENT OBJECTIVE:</b><b>FEES AND EXPENSES:</b><b>Example:</b>115421454643<b>Portfolio Turnover:</b>0043276417040186324726449799178541271315680-0.010.00750.0025<b>INVESTMENT OBJECTIVE:</b>The William Blair Mid Cap Growth Fund seeks long-term capital appreciation.<b>FEES AND EXPENSES:</b>This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.0.002The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 62% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES: </b>0.012<b>PRINCIPAL RISKS OF INVESTING: </b><b>FUND PERFORMANCE HISTORY:</b>122The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.3816601455The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>INVESTMENT OBJECTIVE: </b><b>FEES AND EXPENSES:</b>The William Blair Large Cap Growth Fund seeks long-term capital appreciation.This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.0<b>Example: </b><b>Portfolio Turnover: </b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 50% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES: </b>0.010.00250.00220.01470.0135-0.010.2370.07320.09750.12420.1317-0.37610.389-0.00120.1405-0.01930.1567<b>SUMMARY<br/>WILLIAM BLAIR MID CAP GROWTH FUND</b><b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Total Returns.</b>0.15670.15170.10860.15210.16<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>0.02320.02060.01940.03150.0166Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of medium capitalized ("mid cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of mid cap domestic growth companies that are expected to exhibit quality growth characteristics. For purposes of the Fund, the Advisor considers a company to be a mid cap company if it has a market capitalization no smaller than the smallest capitalized company, and no larger than the largest capitalized company, included in the Russell Midcap&#174; Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to mid cap companies, but that may have a market capitalization above the market capitalization of the largest member, or below the market capitalization of the smallest member, of the Russell Midcap&#174; Index.<br/><br/> The Russell Midcap&#174; Index measures the performance of the 800 companies with the lowest market capitalizations in the Russell 1000&#174; Index. The companies in the Russell Midcap&#174; Index are considered representative of mid cap companies. The size of companies in the Russell Midcap&#174; Index may change with market conditions. In addition, changes to the composition of the Russell Midcap&#174; Index can change the market capitalization range of companies included in the index. As of June 22, 2012, the Russell Midcap&#174; Index included securities issued by companies that ranged in size between $660 million and $20 billion.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor evaluates the extent to which a company meets the quality growth criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be or should have the expectation of becoming, a significant provider in the primary markets it serves, (b) the company should have some distinctive attribute relative to present or potential competitors (this may take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition), (c) the company should participate in an industry expected to grow rapidly due to economic factors or technological change or should grow through market share gains in its industry and (d) the company should have a strong management team.0.07590.07040.0660.07690.071<b>PRINCIPAL RISKS OF INVESTING: </b>The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of large cap domestic growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance. The Fund is designed for long-term investors.<b>FUND PERFORMANCE HISTORY:</b>1374537911747<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">18.57% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(22.57)% (4Q08)</p></td></tr></table>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>SUMMARY<br/>WILLIAM BLAIR LARGE CAP GROWTH FUND</b><b>Shareholder Fees</b> (fees paid directly from your investment)<b>: </b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>: </b>Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of large capitalized ("large cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of large cap domestic growth companies that are expected to exhibit quality growth characteristics. For purposes of the Fund, the Advisor considers a company to be a large cap company if it has a market capitalization no smaller than the smallest capitalized company included in the Russell 1000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to large cap companies, but that may have a market capitalization below the market capitalization of the smallest member of the Russell 1000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index.<br/><br/> The Russell 1000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index is a widely recognized, unmanaged index that measures the performance of the 1,000 largest companies in the Russell 3000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index. The companies in the Russell 1000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index are considered representative of large cap companies. The size of companies in the Russell 1000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index may change with market conditions. In addition, changes to the composition of the Russell 1000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index can change the market capitalization range of the companies included in the index. As of June 22, 2012, the Russell 1000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index included securities issued by companies that ranged in size between $660 million and $544 billion.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor evaluates the extent to which a company meets the quality growth criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be or should have the expectation of becoming, a significant provider in the primary markets it serves, (b) the company should have some distinctive attribute relative to present or potential competitors (this may take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition), (c) the company should participate in an industry expected to grow rapidly due to economic factors or technological change or should grow through market share gains in its industry and (d) the company should have a strong management team.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b> Annual Total Returns.</b><table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly</b><br/> <b>Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">18.02% (1Q12)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(23.78)% (4Q08)</p></td></tr></table><b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>0.13480.10720.09680.1234-0.37710.43750.2276-0.00270.122<b>INVESTMENT OBJECTIVE:</b>0.1220.11760.08510.16130.04230.0380.03550.04070.07340.06770.06310.07072003-12-292003-12-292003-12-292003-12-29<b>INVESTMENT OBJECTIVE: </b>The William Blair International Growth Fund seeks long-term capital appreciation.<b>FEES AND EXPENSES:</b><b>Summary<br/> William Blair Global Small Cap Growth Fund</b>This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.<b>INVESTMENT OBJECTIVE:</b>The William Blair Growth Fund seeks long-term capital appreciation.<b>FEES AND EXPENSES:</b>The William Blair Global Small Cap Growth Fund seeks long-term capital appreciation.<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.<b>Example: </b>This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>Portfolio Turnover: </b>This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 73% of the average value of its portfolio.April 30, 2014<b>Portfolio Turnover: </b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 81% of the average value of its portfolio.0.5The Fund's returns will vary, and you could lose money by investing in the Fund.<b>Shareholder Fees</b> (fees paid directly from your investment):<b>PRINCIPAL INVESTMENT STRATEGIES: </b>April 30, 20140.620The Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Highest Quarterly Return</b>2009-06-300.1857<b>Lowest Quarterly Return</b>-0.2257This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:Under normal market conditions, the Fund invests at least 80% of its total assets in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by companies of all sizes domiciled outside the U.S. that the Advisor believes have above-average growth, profitability and quality characteristics. The Advisor seeks investment opportunities in companies at different stages of development ranging from large, well-established companies to smaller companies at earlier stages of development. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund's investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 35% of its net assets or twice the emerging markets component of the MSCI All Country World Ex-U.S. Investable Market Index (IMI) (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/> The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. Because the Fund is newly organized, portfolio turnover information is not available.The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of foreign companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. These foreign investment risks are magnified in less-established, emerging markets. In addition, the Fund may invest in the securities of smaller companies, which may be more volatile and less liquid than securities of large companies. In addition, smaller companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.<b>FUND PERFORMANCE HISTORY:</b><b>SUMMARY <br/>WILLIAM BLAIR SMALL-MID CAP GROWTH FUND</b><b>PRINCIPAL INVESTMENT STRATEGIES:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>FUND PERFORMANCE HISTORY:</b>The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of domestic growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. The securities of small capitalized ("small cap") and medium capitalized ("mid cap") companies may be more volatile and less liquid than the securities of large capitalized ("large cap") companies. In addition, small and mid cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance. The Fund is designed for long-term investors.The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of domestic growth companies of all sizes that are expected to exhibit quality growth characteristics. The Fund invests primarily in equity securities issued by companies that typically have a market capitalization no smaller than the smallest capitalized company, and no larger than the largest capitalized company, included in the Russell 3000<sup>&#174;</sup> Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects of companies in the Russell 3000<sup>&#174;</sup> Index, but that may have a market capitalization outside the range of companies included in the index.<br/><br/> The Russell 3000<sup>&#174;</sup> Index is a widely recognized, unmanaged index that measures the performance of the 3,000 largest U.S. companies. The size of companies in the Russell 3000<sup>&#174;</sup> Index may change with market conditions. In addition, changes to the composition of the Russell 3000<sup>&#174;</sup> Index can change the market capitalization range of the companies in the index. As of June 22, 2012, the Russell 3000<sup>&#174;</sup> Index included securities issued by companies that ranged in size between $87 million and $544 billion.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor evaluates the extent to which a company meets the quality growth criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be or should have the expectation of becoming, a significant provider in the primary markets it serves, (b) the company should have some distinctive attribute relative to present or potential competitors (this may take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition), (c) the company should participate in an industry expected to grow rapidly due to economic factors or technological change or should grow through market share gains in its industry and (d) the company should have a strong management team.<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b><b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b><b>Annual Total Returns.</b><b>Annual Total Returns.</b>Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small capitalization ("small cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by small cap companies worldwide that the Advisor believes have above average growth, profitability and quality characteristics. For purposes of the Fund, the Advisor considers a company to be a small cap company if it has a float adjusted market capitalization at the time of purchase of $5 billion or less. Securities of companies whose float adjusted market capitalization no longer meets this definition of small cap after purchase may continue to be held in the Fund. The Fund's investments are normally allocated among at least six different countries and no more than 65% of the Fund's equity holdings may be invested in securities of issuers in any one country at any given time. Under normal market conditions at least 40% of the Fund's assets will be invested in companies located outside the United States. Normally, the Fund's investments will be divided among the United States, Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 35% of its net assets or twice the emerging markets component of the MSCI All Country World (ACWI) Small Cap Index (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.<br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of emerging market companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/>The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.<b>PRINCIPAL RISKS OF INVESTING:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the years indicated compare with those of broad measures of market performance. The Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>-0.01The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the last ten calendar years.The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the last ten calendar years.The William Blair International Small Cap Growth Fund seeks long-term capital appreciation.<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>The bar chart and table showing the Fund&#8217;s annual returns and average annual total return are not included because the Fund does not have annual returns for a full calendar year.0.0080.00250.0052This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.0.01570.012-0.0037<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b>0<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>: </b>-0.02This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 76% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES: </b>0.01<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly</b><br/> <b>Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">20.40% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(25.20)% (4Q08)</p></td></tr></table>0.00190.01441224598200.00251836<b>SUMMARY</b><br/><b>WILLIAM BLAIR GROWTH FUND</b>147Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of small capitalization ("small cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by foreign small cap companies, that the Advisor believes have above-average growth, profitability and quality characteristics. For purposes of the Fund, the Advisor considers a company to be a small cap company if it has a float adjusted market capitalization at the time of purchase of $5 billion or less. Securities of companies whose float adjusted market capitalization no longer meets this definition of small cap company after purchase may continue to be held in the Fund. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund's investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 35% of its net assets or twice the emerging markets component of the MSCI All Country World Ex-U.S. Small Cap Index (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.<br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/>The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.<b>PRINCIPAL RISKS OF INVESTING: </b>0.23670.22930.1590.1704-0.0295-0.0331-0.0259-0.02590.09880.0920.08740.1016The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of global small cap companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. These foreign investment risks are magnified in less- established, emerging markets. In addition, the Fund invests primarily in the securities of small cap companies, which may be more volatile and less liquid than securities of large companies. In addition, small cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. These risks are intensified for investments in micro-cap companies (i.e., companies with market capitalizations of $250 million or less). To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Because the Fund is new, investors bear the risk that the Fund may not be able to implement its investment strategies or attract sufficient assets. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.<b>INVESTMENT OBJECTIVE:</b>0.2354The William Blair Small-Mid Cap Growth Fund seeks long-term capital appreciation.0.05230.03690.06340.093-0.377600.31620.1591-0.0364The Fund's returns will vary, and you could lose money by investing in the Fund.-0.010.1831April 30, 2014<b>Shareholder Fees</b> (fees paid directly from your investment):<b>FUND PERFORMANCE HISTORY: </b><b>FEES AND EXPENSES:</b>This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.0.18310.18310.1190.15260.0160.0160.01360.03120.730.05420.05420.04760.0752The Fund's returns will vary, and you could lose money by investing in the Fund.<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment):The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the years indicated compare with those of broad measures of market performance.0.42211-800-635-28860.1848The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.0.2165www.williamblairfunds.com0.2306The Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future.0.1813After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.-0.5233After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.0.42270.2009&#8220;Other Expenses&#8221; are estimated for the current fiscal year since the Fund did not commence operations until April 10, 2013.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.0.0095-0.1451<b>Highest Quarterly Return</b>0.23672009-06-300.00250.204<b>Lowest Quarterly Return</b>2008-12-31The bar chart and table showing the Fund&#8217;s annual returns and average annual total return are not included because the Fund does not have annual returns for a full calendar year.-0.2520.0022This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>0.0142-0.0007The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.0.01350137<b>Portfolio Turnover: </b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairGrowthFund column period compact * ~</div>
-0.02<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualFundOperatingExpensesWilliamBlairGrowthFund column period compact * ~</div>
<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">32.58% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(29.47)% (4Q08)</p></td></tr></table><b>SUMMARY</b><br/><b>WILLIAM BLAIR INTERNATIONAL SMALL CAP GROWTH FUND</b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairGrowthFund column period compact * ~</div>
The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 82% of the average value of its portfolio.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairGrowthFundBarChart column period compact * ~</div>
<b>PRINCIPAL INVESTMENT STRATEGIES: </b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAverageAnnualTotalReturnsTransposedWilliamBlairGrowthFund column period compact * ~</div>
0.1090.10540.07570.15810.04090.04420.03780.03230.05920.05510.05060.0457<b>Highest Quarterly Return</b>0.1802<b>INVESTMENT OBJECTIVE: </b>2012-03-31<b>Lowest Quarterly Return</b>2008-12-31-0.2378The William Blair International Leaders Fund seeks long-term capital appreciation.This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.2006-02-012006-02-012006-02-012006-02-01<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b><b>SUMMARY<br/>WILLIAM BLAIR INTERNATIONAL LEADERS FUND</b>168Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of small capitalized ("small cap") and medium capitalized ("mid cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of small cap and mid cap domestic growth companies that are expected to exhibit quality growth characteristics. For purposes of the Fund, the Advisor considers a company to be a small cap or mid cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to small cap and mid cap companies, but that may have a market capitalization above the market capitalization of the largest member of the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index.<br/><br/> The Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index measures the performance of the 800 companies with the lowest market capitalizations in the Russell 1000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index. The size of companies in the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index may change with market conditions. In addition, changes to the composition of the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index can change the market capitalization range of companies included in the index. As of June 22, 2012, the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index included securities issued by companies that ranged in size between $660 million and $20 billion.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor evaluates the extent to which a company meets the quality growth criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be or should have the expectation of becoming, a significant provider in the primary markets it serves, (b) the company should have some distinctive attribute relative to present or potential competitors (this may take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition), (c) the company should participate in an industry expected to grow rapidly due to economic factors or technological change or should grow through market share gains in its industry and (d) the company should have a strong management team.<b>PRINCIPAL RISKS OF INVESTING: </b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>0.76The Fund's returns will vary, and you could lose money by investing in the Fund.This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal period (August 16, 2012 through December 31, 2012), the Fund&#8217;s portfolio turnover rate was 16% of the average value of its portfolio.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairGlobalSmallCapGrowthFund column period compact * ~</div>
www.williamblair.com<b>PRINCIPAL INVESTMENT STRATEGIES: </b>The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of small cap and mid cap domestic growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. The securities of small cap and mid cap companies may be more volatile and less liquid than securities of large cap companies. In addition, small and mid cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price.<br /><br /> <b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Highest Quarterly Return</b>2009-06-30<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairGlobalSmallCapGrowthFund column period compact * ~</div>
0.3258<b>Lowest Quarterly Return</b>2008-12-31-0.2947<b>FUND PERFORMANCE HISTORY:</b>0.1462-0.3471Under normal market conditions, the Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by companies of all sizes domiciled outside the U.S. that the Advisor believes have above-average growth, profitability and quality characteristics. Under normal market conditions, the Fund typically holds a limited number of securities (i.e., 40-80 securities). The Advisor seeks investment opportunities in companies at different stages of development ranging from large, well-established companies to smaller companies at earlier stages of development, that are leaders in their country, industry or globally in terms of products, services or execution. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund's investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 40% of its net assets or twice the emerging markets component of the MSCI All Country World Ex-U.S. Investable Market Index (IMI) (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.<br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/>The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.0.36030.24010.01650.109The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Total Returns.</b>0.81The Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairMidCapGrowthFund column period compact * ~</div>
After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Highest Quarterly Return</b>2009-06-300.2832<b>Lowest Quarterly Return</b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualFundOperatingExpensesWilliamBlairMidCapGrowthFund column period compact * ~</div>
2008-12-31-0.26550<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairMidCapGrowthFund column period compact * ~</div>
<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairMidCapGrowthFundBarChart column period compact * ~</div>
<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAverageAnnualTotalReturnsTransposedWilliamBlairMidCapGrowthFund column period compact * ~</div>
-0.02<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012).<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">28.32% ( 2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(26.55)% (4Q08)</p></td></tr></table>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">22.08% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(23.38)% (4Q08)</p></td></tr></table>April 30, 20140.82The Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Highest Quarterly Return</b>2009-06-300.2208<b>Lowest Quarterly Return</b>2008-12-31-0.2338<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairSmall-MidCapGrowthFund column period compact * ~</div>
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164The bar chart and table showing the Fund&#8217;s annual returns and average annual total return are not included because the Fund does not have annual returns for a full calendar year.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAverageAnnualTotalReturnsTransposedWilliamBlairInternationalGrowthFund column period compact * ~</div>
<b>SUMMARY</b><br/><b>WILLIAM BLAIR INTERNATIONAL EQUITY FUND</b><b>SUMMARY <br/> WILLIAM BLAIR INTERNATIONAL GROWTH FUND</b><b>INVESTMENT OBJECTIVE:</b>The William Blair International Equity Fund seeks long-term capital appreciation.<b>FEES AND EXPENSES:</b>0.20320.1306-0.51820.5710.2588-0.12160.2073This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>0.0110.003600.01710.01450.06150.05790.05250.0599-0.022005-11-01-0.00260.00950.00250.00570.01770.00250.01450.20730.2030.13830.1852-0.00390.00130.00050.0021-0.0032This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>PRINCIPAL RISKS OF INVESTING: </b>148<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairInternationalSmallCapGrowthFund column period compact * ~</div>
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The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 80% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES: </b><b>Example: </b>Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by foreign large capitalization ("large cap") and medium capitalization ("mid cap") companies that the Advisor believes have above-average growth, profitability and quality characteristics. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund's investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest up to 20% of its net assets in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries. To a limited extent, the Fund may also invest in small capitalization ("small cap") companies.<br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/>The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.<b>PRINCIPAL RISKS OF INVESTING: </b>0.16The Fund's returns will vary, and you could lose money by investing in the Fund.&#8220;Other Expenses&#8221; are estimated for the current fiscal year since the Fund did not commence operations until August 16, 2012.April 30, 2014<b>FUND PERFORMANCE HISTORY:</b>The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of foreign companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. These foreign investment risks are magnified in less-established, emerging markets. In addition, the Fund may invest in the securities of smaller companies, which may be more volatile and less liquid than securities of large companies. In addition, smaller companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br /><br /><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.148The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Total Returns.</b>The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of foreign small cap companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. These foreign investment risks are magnified in less-established, emerging markets. In addition, the Fund invests primarily in the securities of small cap companies, which may be more volatile and less liquid than securities of large companies. In addition, small cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. These risks are intensified for investments in micro-cap companies (i.e., companies with market capitalizations of $250 million or less). To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.0.1350.19960.1768-0.48750.32690.1092-0.12870.1757<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairInternationalLeadersFund column period compact * ~</div>
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The bar chart and table showing the Fund&#8217;s annual returns and average annual total return are not included because the Fund does not have annual returns for a full calendar year.0.17570.16840.11910.1641-0.0503-0.0523-0.0425-0.03430.04010.0370.03460.0598<b>SUMMARY<br/>WILLIAM BLAIR EMERGING MARKETS SMALL CAP GROWTH FUND</b><b>Annual Total Returns. </b><b>PRINCIPAL INVESTMENT STRATEGIES: </b><table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">22.86% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(27.12)% (3Q08)</p></td></tr></table>2004-05-242004-05-242004-05-242004-05-24The William Blair Emerging Markets Growth Fund seeks long-term capital appreciation.This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.<b>INVESTMENT OBJECTIVE:</b>The William Blair Small Cap Value Fund seeks long-term capital appreciation.The William Blair Emerging Markets Small Cap Growth Fund seeks long-term capital appreciation.This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.April 30, 2014The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 90% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES: </b>0.8<b>Example: </b>This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:The Fund's returns will vary, and you could lose money by investing in the Fund.The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 51% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES: </b><b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>0The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<br /><br />www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.<b>PRINCIPAL RISKS OF INVESTING: </b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 78% of the average value of its portfolio.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>PRINCIPAL INVESTMENT STRATEGIES:</b>In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Highest Quarterly Return</b>-0.01Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of emerging market small capitalization ("small cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by emerging market small cap companies that the Advisor believes have above average growth, profitability and quality characteristics. For purposes of the Fund, the Advisor considers a company to be a small cap company if it has a float adjusted market capitalization at the time of purchase no larger than the greater of $3 billion or the largest capitalized company included in the MSCI Emerging Markets Small Cap Index (Net). Securities of companies whose float adjusted market capitalization no longer meets this definition of small cap after purchase may continue to be held in the Fund. Emerging market companies, for purposes of the Fund, are companies organized under the laws of an emerging market country or that have securities traded principally on an exchange or over-the-counter in an emerging market country. Currently, emerging markets include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of emerging market companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/> The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.<b>PRINCIPAL RISKS OF INVESTING:</b><b>INVESTMENT OBJECTIVE:</b>The William Blair Large Cap Value Fund seeks long-term capital appreciation.<b>FEES AND EXPENSES:</b>This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.<b>FUND PERFORMANCE HISTORY: </b>2009-06-300.22860.008<b>Lowest Quarterly Return</b>0.00250.0322008-09-300.04250.012-0.2712The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.0-0.01The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of emerging market small cap companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. These risks may be greatly increased in emerging market countries because the securities of emerging market companies may be subject to greater volatility and less liquidity than companies in more developed markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The currencies of emerging market countries may experience a devaluation relative to the U.S. dollar, and continued devaluations may adversely affect the value of the Fund's assets denominated in such currencies. Many emerging market countries have experienced substantial rates of inflation for many years, and continued inflation may adversely affect the economies and securities markets of such countries. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. In addition, the Fund invests primarily in the securities of small cap companies, which may be more volatile and less liquid than securities of large companies. In addition, small cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. These risks are intensified for investments in micro-cap companies (i.e., companies with market capitalizations of $250 million or less). To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Because the Fund is new, investors bear the risk that the Fund may not be able to implement its investment strategies or attract sufficient assets. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance. The Fund is designed for long-term investors.<b>SUMMARY<br/> WILLIAM BLAIR SMALL CAP VALUE FUND</b><b>Shareholder Fees</b> (fees paid directly from your investment)<b>: </b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>: </b>0.011<b>FUND PERFORMANCE HISTORY:</b>0.0025Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small capitalized ("small cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of small cap domestic companies that the Advisor believes offer a long- term investment value. For purposes of the Fund, the Advisor considers a company to be a small cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell 2000<sup>&#174;</sup> Value Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and value prospects similar to small cap companies, but that may have a market capitalization above the market capitalization of the largest member of the Russell 2000<sup>&#174;</sup> Value Index.<br/><br/> The Russell 2000<sup>&#174;</sup> Value Index is a widely recognized, unmanaged index of common stocks that measures the performance of the small cap value segment of the U.S. equity universe that includes those Russell 2000<sup>&#174;</sup> companies with lower price-to-book ratios and lower forecasted growth values. The companies in the Russell 2000<sup>&#174;</sup> Value Index are considered representative of small cap value companies. The size of companies in the Russell 2000<sup>&#174;</sup> Value Index may change with market conditions. In addition, changes to the composition of the Russell 2000<sup>&#174;</sup> Value Index can change the market capitalization range of the companies included in the index. As of June 22, 2012, the Russell 2000<sup>&#174;</sup> Value Index included securities issued by companies that ranged in size between $100 million and $6 billion.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor evaluates the extent to which a company meets the following criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company's current market value should reflect a material discount from the Advisor's estimate of the company's value, (b) the company should have a reasonable expectation of improving its level of profitability over a three-year investment horizon, (c) the company should have a capable and skilled management team and a clearly articulated and logical business strategy with a reasonable probability of successful execution, (d) the company should have a relatively simple, clean capital structure without excessive use of financial leverage (the company should adhere to conservative and straightforward accounting practices) and (e) there should be a likelihood that the company will undergo a positive corporate change within a three-year investment horizon.0.0024The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>PRINCIPAL RISKS OF INVESTING: </b>0.015900.015-0.02<b>Annual Total Returns.</b>The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of small cap domestic value companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., value vs. growth, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. The securities of small cap companies may be more volatile and less liquid than the securities of large capitalized companies. In addition, small cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. These risks are intensified for investments in micro-cap companies (i.e., companies with market capitalizations of $250 million or less).<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.<b>SUMMARY<br/>WILLIAM BLAIR SMALL-MID CAP VALUE FUND</b>This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:-0.0009<b>FUND PERFORMANCE HISTORY:</b>12210111914The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.4229<b>Annual Total Returns.</b>The bar chart below provides an illustration of the Fund&#8217;s performance in the calendar year since the Fund started.The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the last ten calendar years.153493<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>8571882<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly</b><br/> <b>Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">20.97% (1Q12)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(5.52)% (2Q12)</p></td></tr></table><b> SUMMARY</B><br /><b>WILLIAM BLAIR EMERGING MARKETS GROWTH FUND</b><b>SUMMARY</b><br/><b>WILLIAM BLAIR MID CAP VALUE FUND</b><b>INVESTMENT OBJECTIVE:</b><b>Portfolio Turnover:</b>The William Blair Mid Cap Value Fund seeks long-term capital appreciation.<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b><b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b><b>FEES AND EXPENSES:</b>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b><b>INVESTMENT OBJECTIVE:</b>Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in emerging markets securities. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by emerging market companies of all sizes that the Advisor believes have above-average growth, profitability and quality characteristics. Emerging market companies, for purposes of the Fund, are companies organized under the laws of an emerging market country or that have securities traded principally on an exchange or over-the-counter in an emerging market country. Currently, emerging markets include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time.<br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of emerging market companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/>The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of emerging market companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. These risks may be greatly increased in emerging markets countries because the securities of emerging market companies may be subject to greater volatility and less liquidity than companies in more developed markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The currencies of emerging market countries may experience a devaluation relative to the U.S. dollar, and continued devaluations may adversely affect the value of the Fund's assets denominated in such currencies. Many emerging market countries have experienced substantial rates of inflation for many years, and continued inflation may adversely affect the economies and securities markets of such countries. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. In addition, the Fund may invest in the securities of smaller companies, which may be more volatile and less liquid than securities of large companies. In addition, smaller companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone. </b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.-0.0305The William Blair Small-Mid Cap Value Fund seeks long-term capital appreciation.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Total Returns.</b><b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b><table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">34.01% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(32.72)% (3Q08)</p></td></tr></table><b>FEES AND EXPENSES:</b><b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>: </b>This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 20% of the average value of its portfolio.0.61880.27240.01180.1412<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly</b><br/> <b>Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">25.22% (2Q03)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(23.20)% (4Q08)</p></td></tr></table>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 63% of the average value of its portfolio.-0.0215-0.46850.6955<b>PRINCIPAL INVESTMENT STRATEGIES: </b><b>PRINCIPAL INVESTMENT STRATEGIES:</b>0.16160-0.1331<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>0.1815-0.02This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>SUMMARY<br/>WILLIAM BLAIR BOND FUND</b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 56% of the average value of its portfolio.Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of medium capitalized ("mid cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of mid cap domestic companies that the Advisor believes offer a long-term investment value. For purposes of the Fund, the Advisor considers a company to be a mid cap company if it has a market capitalization no larger than the largest capitalized company, and no smaller than the smallest capitalized company, included in the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Value Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase equity securities of companies with business characteristics and value prospects similar to mid cap companies, but that may have a market capitalization above the market capitalization of the largest member, or below the market capitalization of the smallest member, of the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Value Index.<br/><br/>The Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Value Index is a widely recognized, unmanaged index of common stocks that measures the performance of the mid cap value segment of the U.S. equity universe that includes those Russell Midcap companies with lower price-to-book ratios and lower forecasted growth values. The companies in the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Value Index are considered representative of mid cap value companies. The size of companies in the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Value Index may change with market conditions. In addition, changes to the composition of the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Value Index can change the market capitalization range of the companies included in the index. As of June 22, 2012, the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Value Index included securities issued by companies that ranged in size between $660 million and $18 billion.<br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor evaluates the extent to which a company meets the following criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company's current market value should reflect a material discount from the Advisor's estimate of the company's value, (b) the company should have a reasonable expectation of improving its level of profitability over a three-year investment horizon, (c) the company should have a capable and skilled management team and a clearly articulated and logical business strategy with a reasonable probability of successful execution, (d) the company should have a relatively simple, clean capital structure without excessive use of financial leverage (the company should adhere to conservative and straightforward accounting practices) and (e) there should be a likelihood that the company will undergo a positive corporate change within a three-year investment horizon.<b>PRINCIPAL RISKS OF INVESTING:</b><b>PRINCIPAL INVESTMENT STRATEGIES:</b>The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of mid cap domestic value companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., value vs. growth, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. The securities of mid cap companies may be more volatile and less liquid than the securities of large capitalized companies. In addition, mid cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance. The Fund is designed for long-term investors.00<b>FUND PERFORMANCE HISTORY:</b>0-0.01Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of large capitalized ("large cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of large cap domestic companies that the Advisor believes offer a long-term investment value. These are typically companies that have been financially sound historically, but are temporarily out of favor. For purposes of the Fund, the Advisor considers a company to be a large cap company if it has a market capitalization no smaller than the smallest capitalized company included in the Russell 1000<sup>&#174;</sup> Value Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase equity securities of companies with business characteristics and value prospects similar to large cap companies, but that may have a market capitalization below the market capitalization of the smallest member of the Russell 1000<sup>&#174;</sup> Value Index.<br/><br/> The Russell 1000<sup>&#174;</sup> Value Index is a widely recognized, unmanaged index that measures the performance of the large cap value segment of the U.S. equity universe that includes those Russell 1000<sup>&#174;</sup> companies with lower price-to-book ratios and lower expected growth values. The companies in the Russell 1000<sup>&#174;</sup> Value Index are considered representative of large cap value companies. The size of companies in the Russell 1000<sup>&#174;</sup> Value Index may change with market conditions. In addition, changes to the composition of the Russell 1000<sup>&#174;</sup> Value Index can change the market capitalization range of the companies in the index. As of June 22, 2012, the Russell 1000<sup>&#174;</sup> Value Index included securities issued by companies that ranged in size between $660 million and $384 billion.<br/><br/> The Advisor employs a value-investing approach focusing primarily on established companies that offer capital growth and future dividend payments and whose stock prices appear to be undervalued relative to the general market. In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor begins by screening for stocks whose price-to-earnings ratios are below the average for the Russell 1000<sup>&#174;</sup> Index. The Advisor then compares a company's stock price to its book value, cash flow and free cash flow yield. The Advisor also analyzes individual companies to identify those that are financially sound and appear to have strong potential for long-term growth.<br/><br/> The Advisor assembles the Fund's portfolio from among the most attractive stocks, drawing on an analysis of economic outlooks for various sectors and industries. The Advisor may favor securities from different sectors and industries at different times while maintaining diversification in terms of industries and companies represented. <br/><br/>The Advisor will normally sell a security when the Advisor believes the growth potential or income potential of the security has changed, other investments offer better opportunities or when the Advisor deems the risk/reward potential of the investment to be no longer optimal.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>PRINCIPAL RISKS OF INVESTING:</b>0.0110.0025<b>Annual Total Returns.</b>0.00250.18150.18070.11890.1459The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of large cap domestic value companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., value vs. growth, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Because the Fund is new, investors bear the risk that the Fund may not be able to implement its investment strategies or attract sufficient assets. Separate accounts managed by the Advisor may invest in the Fund, and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance. The Fund is designed for long-term investors.0.0160.0140.01190.01090.0349<b>FUND PERFORMANCE HISTORY: </b>The bar chart below provides an illustration of the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.0.0150.09570.08820.08280.0980.0030.16920.00150.0036The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.0.0081<b>Annual Total Returns.</b><b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairInternationalEquityFund column period compact * ~</div>
0.90.0065-0.001The Fund's returns will vary, and you could lose money by investing in the Fund.The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualFundOperatingExpensesWilliamBlairInternationalEquityFund column period compact * ~</div>
Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small capitalized ("small cap") and medium capitalized ("mid cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of small cap and mid cap domestic companies that the Advisor believes offer a long-term investment value. For purposes of the Fund, the Advisor considers a company to be a small cap or mid cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Value Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase equity securities of companies with business characteristics and value prospects similar to small and mid cap companies, but that may have a market capitalization above the market capitalization of the largest member of the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Value Index.<br/><br/> The Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Value Index is a widely recognized, unmanaged index of common stocks that includes those Russell Midcap companies with lower price-to-book ratios and lower forecasted growth values. The size of companies in the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Value Index may change with market conditions. In addition, changes to the composition of the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Value Index can change the market capitalization range of the companies included in the index. As of June 22, 2012, the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Value Index included securities issued by companies that ranged in size between $660 million and $18 billion.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor evaluates the extent to which a company meets the following criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company's current market value should reflect a material discount from the Advisor's estimate of the company's value, (b) the company should have a reasonable expectation of improving its level of profitability over a three-year investment horizon, (c) the company should have a capable and skilled management team and a clearly articulated and logical business strategy with a reasonable probability of successful execution, (d) the company should have a relatively simple, clean capital structure without excessive use of financial leverage (the company should adhere to conservative and straightforward accounting practices) and (e) there should be a likelihood that the company will undergo a positive corporate change within a three-year investment horizon.www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.-0.0016After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.<b>PRINCIPAL RISKS OF INVESTING:</b>After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairInternationalEquityFund column period compact * ~</div>
<b>Highest Quarterly Return</b>2009-06-30<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly</b><br/> <b>Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">14.67% (1Q12)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(4.82)% (2Q12)</p></td></tr></table>0.3401<b>Lowest Quarterly Return</b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairInternationalEquityFundBarChart column period compact * ~</div>
2008-09-30-0.3272<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">14.09% (4Q11)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(17.49)% (3Q11)</p></td></tr></table><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAverageAnnualTotalReturnsTransposedWilliamBlairInternationalEquityFund column period compact * ~</div>
1530.011The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of small cap and mid cap domestic value companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., value vs. growth, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. The securities of small cap and mid cap companies may be more volatile and less liquid than the securities of large capitalized companies. In addition, small and mid cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider the Fund for the aggressive portion of your portfolio. Because the Fund is new, investors bear the risk that the Fund may not be able to implement its investment strategies or attract sufficient assets. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.00.0025-0.01<b>SUMMARY<br/>WILLIAM BLAIR SMALL CAP GROWTH FUND </b>0.03410.0476<b>INVESTMENT OBJECTIVE:</b>The William Blair Small Cap Growth Fund seeks long-term capital appreciation.-0.03110.0165<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>FUND PERFORMANCE HISTORY:</b>0.12490.12320.08350.18050.05110.04920.04380.03550.00950The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.66<b>FEES AND EXPENSES:</b>0.08760.06950.0710.095<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b>-0.02This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>0.00250.0220.034<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b>0.01350.17510.11190.16780.16920.011<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>0.13870.13710.1180.1613168<b>Annual Total Returns.</b>0.08330.07410.07860.0025This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:0.11110.01640.0034-0.02050.0169The bar chart below provides an illustration of the Fund&#8217;s performance in the calendar year since the Fund started.The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 89% of the average value of its portfolio.0.39310.1205<b>PRINCIPAL INVESTMENT STRATEGIES: </b>0.00490.2178-0.0554-0.25850.26241370.3094-0.06950.08330.06720.05530.04210.12490.07230.05550.05230.05951720.06970.05320.05030.06110.3423Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of small capitalized ("small cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of small cap domestic growth companies that are expected to exhibit quality growth characteristics. The Fund's investments in small cap companies may include a significant weighting to micro-cap companies (i.e., those with market capitalizations of $250 million or less at the time of the Fund's investment). For purposes of the Fund, the Advisor considers a company to be a small cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to small cap companies, but that may have a market capitalization above the market capitalization of the largest member of the Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index.<br/><br/> The Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index is a widely recognized, unmanaged index of common stocks that measures the performance of the 2,000 smallest companies in the Russell 3000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index. The companies in the Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index are considered representative of small cap companies. The size of companies in the Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index may change with market conditions. In addition, changes to the composition of the Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index can change the market capitalization range of the companies included in the index. As of June 22, 2012, the Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index included securities issued by companies that ranged in size between $87 million and $6 billion. <br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor evaluates the extent to which a company meets the quality growth criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be or should have the expectation of becoming, a significant provider in the primary markets it serves, (b) the company should have some distinctive attribute relative to present or potential competitors (this may take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition), (c) the company should participate in an industry expected to grow rapidly due to economic factors or technological change or should grow through market share gains in its industry and (d) the company should have a strong management team.<b>PRINCIPAL RISKS OF INVESTING: </b>0.34230.34120.22390.2222-0.00340.25190.25110.21480.12050.1354<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">9.67% (1Q12)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(4.62)% (2Q12)</p></td></tr></table><b>PRINCIPAL RISKS OF INVESTING: </b>0.01The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of small cap domestic growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. The securities of small cap companies may be more volatile and less liquid than securities of large cap companies. In addition, small cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. These risks are intensified for investments in micro-cap companies.<br/><br/> <b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.0.00252010-05-032010-05-032010-05-032010-05-032007-05-012007-05-012007-05-01<b>FUND PERFORMANCE HISTORY:</b>0.00410.01660.2070.20610.13580.1868<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012).-0.0388-0.0479-0.0357-0.0070.0165<b>Annual Total Returns.</b>2011-10-242011-10-242011-10-24The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the last ten calendar years.2007-05-0100.13540.09780.12810.18510.07490.07930.06780.0881<b>PRINCIPAL RISKS OF INVESTING: </b>-0.0001-0.010.11110.0980.09460.115<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.0.010.00250.2<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">37.12% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(29.92)% (4Q08)</p></td></tr></table>0.0509April 30, 20140.0634The Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886www.williamblair.com-0.0494The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.April 30, 20140.78The Fund's returns will vary, and you could lose money by investing in the Fund.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.-0.04820.0142012-06-30<b>Lowest Quarterly Return</b>0.14672012-03-31<b>Highest Quarterly Return</b>April 30, 2014The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.0.512005-06-062005-06-062005-06-062005-06-06The Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.0After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.0In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.<b>Highest Quarterly Return</b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairMidCapValueFund column period compact * ~</div>
2003-06-30The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.1-800-635-28861430.2522<b>Lowest Quarterly Return</b>www.williamblair.com2008-12-31<b>Portfolio Turnover:</b>-0.2322011-10-242011-10-242011-10-242011-10-24<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualFundOperatingExpensesWilliamBlairMidCapValueFund column period compact * ~</div>
0.00420.0026<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairMidCapValueFund column period compact * ~</div>
0.0083After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairMidCapValueFundBarChart column period compact * ~</div>
0.00150.1195<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAverageAnnualTotalReturnsTransposedWilliamBlairMidCapValueFund column period compact * ~</div>
<b>FUND PERFORMANCE HISTORY:</b>0.3790.11950.10960.08140.19210.16180.15190.13350.2303The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of foreign companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Because the Fund may focus its investments in a limited number of securities, its performance may be more volatile than a fund that invests in a greater number of securities. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. These foreign investment risks are magnified in less-established, emerging markets. In addition, the Fund may invest in the securities of smaller companies, which may be more volatile and less liquid than securities of large companies. In addition, smaller companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone. </b> You should only consider it for the aggressive portion of your portfolio. Because the Fund is new, investors bear the risk that the Fund may not be able to implement its investment strategies or attract sufficient assets. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.85After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.0.3775<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairLargeCapValueFund column period compact * ~</div>
-0.61710.73850.2344-0.17290.060.04760.03890.03890.207<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairSmallCapValueFund column period compact * ~</div>
0.04850.03330.03240.0518<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualFundOperatingExpensesWilliamBlairLargeCapValueFund column period compact * ~</div>
0.03750.02050.02170.0462<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualFundOperatingExpensesWilliamBlairSmallCapValueFund column period compact * ~</div>
<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairLargeCapValueFund column period compact * ~</div>
<b>Highest Quarterly Return</b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairSmallCapValueFund column period compact * ~</div>
2012-03-31<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairLargeCapValueFundBarChart column period compact * ~</div>
0.2097<b>Lowest Quarterly Return</b>2012-06-30<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairSmallCapValueFundBarChart column period compact * ~</div>
-0.0552April 30, 2014<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAverageAnnualTotalReturnsTransposedWilliamBlairLargeCapValueFund column period compact * ~</div>
0.89<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAverageAnnualTotalReturnsTransposedWilliamBlairSmallCapValueFund column period compact * ~</div>
<b>Example: </b>The Fund's returns will vary, and you could lose money by investing in the Fund.<b>SUMMARY</b><br/><b>WILLIAM BLAIR LARGE CAP VALUE FUND </b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairEmergingMarketsGrowthFund column period compact * ~</div>
The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.2011-12-152011-12-152011-12-152011-12-151-800-635-2886April 30, 2014www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.0.63<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualFundOperatingExpensesWilliamBlairEmergingMarketsGrowthFund column period compact * ~</div>
The Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886www.williamblair.com<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairEmergingMarketsGrowthFund column period compact * ~</div>
The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairEmergingMarketsGrowthFundBarChart column period compact * ~</div>
After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Highest Quarterly Return</b>In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.2011-12-31<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAverageAnnualTotalReturnsTransposedWilliamBlairEmergingMarketsGrowthFund column period compact * ~</div>
0.1409<b>Highest Quarterly Return</b>2009-06-30<b>Lowest Quarterly Return</b>2011-09-300.37120.03680.0261<b>Lowest Quarterly Return</b>-0.17492008-12-310.0171-0.29920.04250.0108-0.02460.09880.0604<b>INVESTMENT OBJECTIVE:</b>0.05210.06The William Blair Bond Fund seeks to outperform the Barclays Capital U.S. Aggregate Index by maximizing total return through a combination of income and capital appreciation.<b>FEES AND EXPENSES:</b><b>Example:</b>This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairSmallCapGrowthFund column period compact * ~</div>
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The bar chart below provides an illustration of the Fund&#8217;s performance in the calendar year since the Fund started.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairSmallCapGrowthFundBarChart column period compact * ~</div>
<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAverageAnnualTotalReturnsTransposedWilliamBlairSmallCapGrowthFund column period compact * ~</div>
<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairEmergingMarketsSmallCapGrowthFund column period compact * ~</div>
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<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairEmergingMarketsSmallCapGrowthFund column period compact * ~</div>
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This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairIncomeFund column period compact * ~</div>
The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 25% of the average value of its portfolio.<b>Portfolio Turnover: </b><b>FEES AND EXPENSES:</b><b>PRINCIPAL INVESTMENT STRATEGIES: </b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairIncomeFundBarChart column period compact * ~</div>
<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAverageAnnualTotalReturnsTransposedWilliamBlairIncomeFund column period compact * ~</div>
Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in bonds. Other types of income producing securities, such as convertible bonds, hybrid bonds and preferred stock, may also be considered in seeking to achieve the Fund's investment objective. The Fund's investments may have variable rates of interest. The Fund invests primarily in U.S. dollar denominated, investment grade fixed income securities. A security is considered to be investment grade if it is rated in one of the highest four categories by at least one of the following three nationally recognized statistical rating organizations: Fitch Ratings, Moody's Investors Service, Inc. and Standard &amp; Poor's, a division of The McGraw-Hill Companies, Inc. (the "Rating Organizations"). No more than 10% of the Fund's net assets may be invested in below investment grade securities (e.g., high yield or junk bonds), which are securities rated below Baa/BBB, provided that the securities are rated "B &#8211;" or better by each of the Rating Organizations issuing a rating, or, if unrated, that the Advisor deems such securities to be of at least "B &#8211;" quality at the time of purchase. The Fund's investments in below investment grade securities may have additional credit risk. In some cases, below investment grade securities may decline in credit quality or go into default.<br/><br/>The Fund's assets will principally be invested in obligations of, or guaranteed by, the U.S. Government, its agencies or instrumentalities; corporate debt securities issued by domestic and foreign companies; and mortgage-backed securities and asset-backed securities, which are debt securities issued by a corporation, trust or custodian, or by a U.S. Government agency or instrumentality, that are collateralized (i.e., secured as to payment of interest and/or principal) by a portfolio or pool of assets, such as mortgages, debit balances on credit card accounts or U.S. Government securities. The Fund may also invest in Rule 144A securities.<br/><br/>The anticipated average duration for the Fund is a range within one year longer or shorter than the average duration of the Barclays U.S. Aggregate Index (the "Benchmark"). As of March 31, 2013, the modified adjusted duration of the Benchmark was 5.26 years. The duration of an instrument is different from the maturity of an instrument in that duration measures the average period remaining until the discounted value of the amounts due (principal and interest) under the instrument are to be paid, rather than the instrument's stated final maturity. In addition, portfolio duration of five years means that if interest rates increased by one percent, the value of the portfolio would decrease by approximately five percent. For purposes of calculating duration, instruments allowing prepayment will be assigned a prepayment schedule by the Advisor based upon industry experience.<br/><br/>The Advisor emphasizes individual security selection, as well as shifts in the Fund's portfolio among market sectors. To a lesser extent, the Advisor actively manages the Fund's average duration relative to the Benchmark. The Fund does not invest in common stocks, foreign currency denominated securities or securities of which the coupon or principal payments are determined by commodity or equity indices.<b>PRINCIPAL RISKS OF INVESTING: </b>2005-11-012005-11-012005-11-01The Fund is subject to credit risk. The Fund's net asset value and total return may be adversely affected by the inability of the issuers of the Fund's securities to make interest payments or payment at maturity. The Fund's investments in obligations issued or guaranteed by U.S. Government agencies or instrumentalities may not be backed by the full faith and credit of the United States and may differ in the degree of support provided by the U.S. Government. The Fund is also subject to interest rate risk. The value of income producing securities will generally decrease when interest rates rise, which means the Fund's net asset value and total returns will likewise decrease in a rising interest rate environment. As of the date of this Prospectus, interest rates continue to be at historic lows. Investments with longer maturities, which typically provide higher yields than securities with shorter maturities, may subject the Fund to increased price changes resulting from market yield fluctuations. The Fund's investments in mortgage-backed securities and asset-backed securities are subject to prepayment and extension risk. Prepayment of high interest rate mortgage-backed securities and asset-backed securities during times of declining interest rates will tend to lower the return of the Fund and may even result in losses to the Fund if the prepaid securities were acquired at a premium. Slower prepayments during periods of rising interest rates may increase the duration of the Fund's mortgage-backed securities and asset-backed securities and reduce their value. Rule 144A securities are not registered for resale in the general securities market and may be classified as illiquid. The Fund's investments in below investment grade securities may be less liquid than investment grade securities. It may not be possible to sell or otherwise dispose of illiquid securities both at the price and within a time period deemed desirable by the Fund. <br/><br/>The Fund is also subject to income risk, which is the risk that the income received by the Fund may decrease as a result of a decline in interest rates. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Thus, the Fund's returns will vary, and you could lose money by investing in the Fund. Of course, for all mutual funds there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance.<b>FUND PERFORMANCE HISTORY:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairLargeCapGrowthFund column period compact * ~</div>
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<b>INVESTMENT OBJECTIVE: </b>The William Blair Low Duration Fund seeks to maximize total return. Total return includes both income and capital appreciation.<b>FEES AND EXPENSES:</b>This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.<b>Example: </b>This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 20% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES: </b><b>PRINCIPAL RISKS OF INVESTING: </b><b>FUND PERFORMANCE HISTORY:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with that of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Total Returns. </b>The bar chart below provides an illustration of the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>SUMMARY</b><br /><b>WILLIAM BLAIR READY RESERVES FUND</b><b>INVESTMENT OBJECTIVE:</b>The William Blair Ready Reserves Fund seeks current income, a stable share price and daily liquidity.<b>FEES AND EXPENSES:</b>This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.<b>Shareholder Fees</b> (fees paid directly from your investment)<b>: </b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b><b>Example: </b>This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>PRINCIPAL INVESTMENT STRATEGIES: </b>The Fund invests primarily in short-term U.S. dollar-denominated domestic money market instruments, which include securities issued by domestic companies; the U.S. Government, its agencies and instrumentalities; and U.S. banks. The Fund invests exclusively in securities that are high quality, which means that they are rated in the top two categories by a nationally recognized statistical rating organization. The Fund reserves the right to invest more than 25% of its assets in the domestic banking industry. The Fund may also invest in U.S. dollar-denominated money market instruments issued by foreign banks, foreign governments and multinational organizations, such as the World Bank. The Fund may also invest in asset-backed securities, repurchase agreements, Section 4(2) commercial paper, when-issued and delayed delivery securities and variable rate securities, each of which is more fully described in the Investment Glossary. The Fund is designed to be highly liquid and seeks to maintain a net asset value of $1.00 per share although there is no guarantee that the net asset value of $1.00 per share of the Fund will be maintained. The Fund is designed for investors who seek to obtain the maximum current income consistent with the preservation of capital.<b>PRINCIPAL RISKS OF INVESTING: </b>Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund. As with any money market fund, there is a risk that the issuers or guarantors of securities will default on the payment of principal or interest or the obligation to repurchase securities from the Fund. An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You should not rely on or expect the Advisor to purchase distressed assets, make capital infusions, enter into support agreements or take other actions to maintain the Fund's $1.00 share price. The credit quality of the Fund's holdings can change rapidly in certain markets, and the default of a single holding could have an adverse impact on the Fund's share price. To the extent the Fund invests in short-term U.S. dollar-denominated foreign money market instruments, investing in foreign securities may involve a greater degree of risk than investing in domestic securities due to the possibility of, but not limited to, less publicly available information, more volatile markets, less securities regulation, less favorable tax provisions, war and expropriation. The Fund's share price can also be negatively affected during periods of high redemption pressures and/or illiquid markets. The actions of a few large investors in the Fund may have a significant adverse effect on the share price of the Fund. Because the Fund may concentrate its assets in the banking industry, the Fund's performance may depend in large part on that industry. Of course, for all mutual funds there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result.<b>FUND PERFORMANCE HISTORY:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Total Returns.</b>The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the last ten calendar years.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairLowDurationFund column period compact * ~</div>
The William Blair Growth Fund seeks long-term capital appreciation.This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.<b>Average Annual Total Returns </b> (For the periods ended December 31, 2012).<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualFundOperatingExpensesWilliamBlairLowDurationFund column period compact * ~</div>
<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairLowDurationFund column period compact * ~</div>
<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">1.18% (4Q06)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">0.00% (4Q09)</p></td></tr></table><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairLowDurationFundBarChart column period compact * ~</div>
The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 73% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES: </b>This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>PRINCIPAL RISKS OF INVESTING: </b><b>SUMMARY</b><br/><b>WILLIAM BLAIR LOW DURATION FUND</b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualFundOperatingExpensesWilliamBlairGlobalSmallCapGrowthFund column period compact * ~</div>
<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>The Fund seeks to maximize total return by investing in a diversified portfolio of investment grade low duration debt securities. Total return includes both income and capital appreciation. The Fund seeks to outperform the Bank of America Merrill Lynch 1-Year U.S. Treasury Note Index through an actively managed diversified portfolio of securities. The Advisor emphasizes individual security selection, as well as shifts in the Fund's portfolio among market sectors. The Advisor also actively manages the Fund's average duration relative to the Bank of America Merrill Lynch 1-Year U.S. Treasury Note Index.<br/><br/>The Fund invests primarily in investment grade debt securities rated in the highest three categories by at least one of the following three nationally recognized statistical rating organizations: Fitch Ratings, Moody's Investors Service, Inc. and Standard &amp; Poor's, a division of The McGraw-Hill Companies, Inc.<br/><br/>The Fund invests in U.S. dollar denominated securities. The Fund's assets will principally be invested in the following: (1) obligations of or guaranteed by the U.S. Government, its agencies or instrumentalities; (2) corporate debt securities issued by domestic or foreign companies; (3) mortgage-backed securities and asset-backed securities, which are debt securities issued by a corporation, trust or custodian, or by a U.S. Government agency or instrumentality, that are collateralized (i.e., secured as to payment of interest and/or principal) by a portfolio or pool of assets, such as mortgages, debit balances on credit card accounts or U.S. Government securities; and (4) money market instruments, including, but not limited to, those issued by domestic companies, the U.S. Government and its agencies and instrumentalities, U.S. banks and municipalities. The Fund may also invest in Rule 144A securities.<br/><br/>The anticipated weighted average duration for the Fund is between 0.5 to 2 years. The duration of an instrument is different from the maturity of an instrument in that duration measures the average period remaining until the discounted value of the amounts due (principal and interest) under the instrument are to be paid, rather than the instrument's stated final maturity. In addition, portfolio duration of two years means that if interest rates increased by one percent, the value of the portfolio would decrease by approximately two percent. For purposes of calculating duration, instruments allowing prepayment will be assigned a prepayment schedule by the Advisor based upon industry experience.<br/><br/>The Fund may also invest in U.S. dollar-denominated money market instruments issued by foreign banks, foreign governments and multinational organizations, such as the World Bank. The Fund may also invest in Section 4(2) commercial paper. The Fund does not invest in common stocks, foreign currency denominated securities or securities of which the coupon or principal payments are determined by commodity or equity indices.The Fund is subject to credit risk. The Fund's net asset value and total return may be adversely affected by the inability of the issuers of the Fund's securities to make interest payments or payment at maturity. The Fund's investments in obligations issued or guaranteed by U.S. Government agencies or instrumentalities may not be backed by the full faith and credit of the United States and may differ in the degree of support provided by the U.S. Government. The Fund is also subject to interest rate risk. The value of income producing securities will generally decrease when interest rates rise, which means the Fund's net asset value and total returns will likewise decrease in a rising interest rate environment. As of the date of this Prospectus, interest rates continue to be at historic lows. Investments with longer maturities, which typically provide higher yields than securities with shorter maturities, may subject the Fund to increased price changes resulting from market yield fluctuations. The Fund's investments in mortgage-backed securities and asset-backed securities are subject to prepayment and extension risk. Prepayment of high interest rate mortgage-backed securities and asset-backed securities during times of declining interest rates will tend to lower the return of the Fund and may even result in losses to the Fund if the prepaid securities were acquired at a premium. Slower prepayments during periods of rising interest rates may increase the duration of the Fund's mortgage-backed securities and asset-backed securities and reduce their value. Rule 144A securities are not registered for resale in the general securities market and may be classified as illiquid. It may not be possible to sell or otherwise dispose of illiquid securities both at the price and within the time period deemed desirable by the Fund. The Fund is also subject to income risk, which is the risk that the income received by the Fund may decrease as a result of a decline in interest rates. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Thus, the Fund's returns will vary, and you could lose money by investing in the Fund. Of course, for all mutual funds there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance.<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b><b>Yield:</b> You may obtain the most current yield information for the Fund by calling 1-800-742-7272.<b>Annual Total Returns.</b><table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">1.15% (3Q12)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">0.04% (4Q12)</p></td></tr></table><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAverageAnnualTotalReturnsTransposedWilliamBlairLowDurationFund column period compact * ~</div>
The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the last ten calendar years.000.0030.00150.002900.00740.0070<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>0.00240.00030.006200.0035-0.0004631993467740.01860.01730.028<b>SUMMARY<br/>WILLIAM BLAIR LARGE CAP GROWTH FUND</b><b>INVESTMENT OBJECTIVE: </b>The William Blair Large Cap Growth Fund seeks long-term capital appreciation.This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.72233408915<b>Example: </b>This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:0.00660.008The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 50% of the average value of its portfolio.0.0280.01850.01820.00240.01870.01020.0110.0048-0.010.02620.04470.04750.0220.0010.00010.00010.00012009-12-012009-12-012009-12-012009-12-010.0075<b>PRINCIPAL RISKS OF INVESTING: </b>00.00140.0089910.00010.00012840.00470.00494930.01550.01521096<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of large capitalized ("large cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of large cap domestic growth companies that are expected to exhibit quality growth characteristics. For purposes of the Fund, the Advisor considers a company to be a large cap company if it has a market capitalization no smaller than the smallest capitalized company included in the Russell 1000<sup>&#174;</sup> Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to large cap companies, but that may have a market capitalization below the market capitalization of the smallest member of the Russell 1000<sup>&#174;</sup> Index.<br/><br/>The Russell 1000<sup>&#174;</sup> Index is a widely recognized, unmanaged index that measures the performance of the 1,000 largest companies in the Russell 3000<sup>&#174;</sup> Index. The companies in the Russell 1000<sup>&#174;</sup> Index are considered representative of large cap companies. The size of companies in the Russell 1000<sup>&#174;</sup> Index may change with market conditions. In addition, changes to the composition of the Russell 1000<sup>&#174;</sup> Index can change the market capitalization range of the companies included in the index. As of June 22, 2012, the Russell 1000<sup>&#174;</sup> Index included securities issued by companies that ranged in size between $660 million and $544 billion.<br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor evaluates the extent to which a company meets the quality growth criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be or should have the expectation of becoming, a significant provider in the primary markets it serves, (b) the company should have some distinctive attribute relative to present or potential competitors (this may take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition), (c) the company should participate in an industry expected to grow rapidly due to economic factors or technological change or should grow through market share gains in its industry and (d) the company should have a strong management team.The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of large cap domestic growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance. The Fund is designed for long-term investors.<b>FUND PERFORMANCE HISTORY:</b><b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Total Returns. </b>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.0.16030.1550.11130.15210.16The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-28860.02650.02390.02230.03150.0166www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.0.07920.07380.0690.07690.0710.2April 30, 2014Thus, the Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with that of a broad measure of market performance.1-800-635-2886www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.<b>Highest Quarterly Return</b>02012-09-300.0115<b>Lowest Quarterly Return</b>2012-12-310.0004After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.-0.01After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>Highest&nbsp;Quarterly Return</b>2006-12-31In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.0.0118<b>Lowest&nbsp;Quarterly Return</b>2009-12-3100.00800.0043You may obtain the most current yield information for the Fund0.01231-800-742-72720.0095-0.0028<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairReadyReservesFund column period compact * ~</div>
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<b>SUMMARY</b><br /><b>WILLIAM BLAIR GROWTH FUND </b><b>Shareholder Fees</b> (fees paid directly from your investment):<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment):The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of domestic growth companies of all sizes that are expected to exhibit quality growth characteristics. The Fund invests primarily in equity securities issued by companies that typically have a market capitalization no smaller than the smallest capitalized company, and no larger than the largest capitalized company, included in the Russell 3000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects of companies in the Russell 3000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index, but that may have a market capitalization outside the range of companies included in the index.<br/><br/>The Russell 3000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index is a widely recognized, unmanaged index that measures the performance of the 3,000 largest U.S. companies. The size of companies in the Russell 3000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index may change with market conditions. In addition, changes to the composition of the Russell 3000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index can change the market capitalization range of the companies in the index. As of June 22, 2012, the Russell 3000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index included securities issued by companies that ranged in size between $87 million and $544 billion.<br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor evaluates the extent to which a company meets the quality growth criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be or should have the expectation of becoming, a significant provider in the primary markets it serves, (b) the company should have some distinctive attribute relative to present or potential competitors (this may take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition), (c) the company should participate in an industry expected to grow rapidly due to economic factors or technological change or should grow through market share gains in its industry and (d) the company should have a strong management team.The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of domestic growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. The securities of small capitalized ("small cap") and medium capitalized ("mid cap") companies may be more volatile and less liquid than the securities of large capitalized ("large cap") companies. In addition, small and mid cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance. The Fund is designed for long-term investors.<b>FUND PERFORMANCE HISTORY:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the years indicated compare with those of broad measures of market performance. The Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly</b><br/> <b>Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">20.61% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(25.07)% (4Q08)</p></td></tr></table><b>Average Annual Total Returns</b> (For the periods ended December 31, 2012).The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly</b><br/> <b>Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">18.21% (1Q12)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(23.68)% (4Q08)</p></td></tr></table>0.18780.18780.1220.15260.03120.0160.01870.01860.05690.05690.050.0752<b>Portfolio Turnover: </b>0.73The Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the years indicated compare with those of broad measures of market performance.1-800-635-2886www.williamblairfunds.comThe Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Highest Quarterly Return</b>2009-06-300.2061<b>Lowest Quarterly Return</b>2008-12-31-0.2507<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairGrowthFundClassI column period compact * ~</div>
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0.24140.07540.10010.12640.1359-0.37350.39340.1436-0.0160.16030.24270.05340.03960.06550.0936-0.37560.32170.1603-0.03540.1878<b>INVESTMENT OBJECTIVE:</b>The William Blair Mid Cap Growth Fund seeks long-term capital appreciation.<b>FEES AND EXPENSES:</b>This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.<b>Example: </b>This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>Portfolio Turnover: </b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 62% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES: </b><b>SUMMARY</b><br/><b>WILLIAM BLAIR SMALL CAP GROWTH FUND</b><b>INVESTMENT OBJECTIVE:</b>The William Blair Small Cap Growth Fund seeks long-term capital appreciation.<b>SUMMARY<br/>WILLIAM BLAIR INTERNATIONAL SMALL CAP GROWTH FUND</b><b>FEES AND EXPENSES</b><b>:</b>This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.<b>FEES AND EXPENSES:</b>The Fund's returns will vary, and you could lose money by investing in the Fund.<b>PRINCIPAL RISKS OF INVESTING: </b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886www.williamblair.comThe Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of mid cap domestic growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. The securities of mid cap companies may be more volatile and less liquid than securities of large cap companies. In addition, mid cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance. The Fund is designed for long-term investors.<b>Shareholder Fees</b> (fees paid directly from your investment)<b>: </b>The Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.<b>FUND PERFORMANCE HISTORY:</b>After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Highest Quarterly Return</b>2012-03-31<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>: </b>0.1821<b>Annual Total Returns.</b><b>Lowest Quarterly Return<b>2008-12-31The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.-0.2368<b>Example: </b>This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:0.5<b>Portfolio Turnover: </b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 89% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES: </b>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>INVESTMENT OBJECTIVE:</b>The William Blair Small-Mid Cap Growth Fund seeks long-term capital appreciation.<b>SUMMARY</b><br/><b>WILLIAM BLAIR INTERNATIONAL LEADERS FUND</b><b>FEES AND EXPENSES:</b>This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.The William Blair International Leaders Fund seeks long-term capital appreciation.<b>FEES AND EXPENSES:</b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairLargeCapGrowthFundClassI column period compact * ~</div>
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<b>INVESTMENT OBJECTIVE:</b>The William Blair International Equity Fund seeks long-term capital appreciation.<b>FEES AND EXPENSES:</b>This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.<b>SUMMARY<br/>WILLIAM BLAIR INTERNATIONAL GROWTH FUND</b><b>Shareholder Fees</b> (fees paid directly from your investment)<b>: </b>The William Blair International Growth Fund seeks long-term capital appreciation.<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>: </b><b>INVESTMENT OBJECTIVE:</b>April 30, 2014This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.<b>Example: </b>This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of small capitalized ("small cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of small cap domestic growth companies that are expected to exhibit quality growth characteristics. The Fund's investments in small cap companies may include a significant weighting to micro-cap companies (i.e., those with market capitalizations of $250 million or less at the time of the Fund's investment). For purposes of the Fund, the Advisor considers a company to be a small cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to small cap companies, but that may have a market capitalization above the market capitalization of the largest member of the Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index.<br/><br/>The Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index is a widely recognized, unmanaged index of common stocks that measures the performance of the 2,000 smallest companies in the Russell 3000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index. The companies in the Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index are considered representative of small cap companies. The size of companies in the Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index may change with market conditions. In addition, changes to the composition of the Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index can change the market capitalization range of the companies included in the index. As of June 22, 2012, the Russell 2000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index included securities issued by companies that ranged in size between $87 million and $6 billion.<br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor evaluates the extent to which a company meets the quality growth criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be or should have the expectation of becoming, a significant provider in the primary markets it serves, (b) the company should have some distinctive attribute relative to present or potential competitors (this may take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition), (c) the company should participate in an industry expected to grow rapidly due to economic factors or technological change or should grow through market share gains in its industry and (d) the company should have a strong management team.The William Blair International Small Cap Growth Fund seeks long-term capital appreciation.<b>PRINCIPAL RISKS OF INVESTING: </b><b>Portfolio Turnover: </b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 80% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES: </b><b>FEES AND EXPENSES:</b><b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b>The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of small cap domestic growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. The securities of small cap companies may be more volatile and less liquid than securities of large cap companies. In addition, small cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. These risks are intensified for investments in micro-cap companies.<br /><br /><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.<b>FUND PERFORMANCE HISTORY:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b><b>Annual Total Returns.</b>The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the last ten calendar years.<b>Shareholder Fees</b> (fees paid directly from your investment)<b>: </b>Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by foreign large capitalization ("large cap") and medium capitalization ("mid cap") companies that the Advisor believes have above-average growth, profitability and quality characteristics. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund's investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest up to 20% of its net assets in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries. To a limited extent, the Fund may also invest in small capitalization ("small cap") companies.<br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/>The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b><b>PRINCIPAL RISKS OF INVESTING: </b><b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b><b>Example:</b>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>Portfolio Turnover:</b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal period (August 16, 2012 through December 31, 2012), the Fund&#8217;s portfolio turnover rate was 16% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES:</b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>: </b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>Example: </b><table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">37.26% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(29.84)% (4Q08)</p></td></tr></table>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 81% of the average value of its portfolio.This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>PRINCIPAL INVESTMENT STRATEGIES: </b><b>Portfolio Turnover: </b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 76% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES: </b>Under normal market conditions, the Fund invests at least 80% of its total assets in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by companies of all sizes domiciled outside the U.S. that the Advisor believes have above-average growth, profitability and quality characteristics. The Advisor seeks investment opportunities in companies at different stages of development ranging from large, well-established companies to smaller companies at earlier stages of development. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund's investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 35% of its net assets or twice the emerging markets component of the MSCI All Country World Ex-U.S. Investable Market Index (IMI) (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/> The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.<b>PRINCIPAL RISKS OF INVESTING: </b>The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the last ten calendar years.Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of small capitalization ("small cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by foreign small cap companies, that the Advisor believes have above-average growth, profitability and quality characteristics. For purposes of the Fund, the Advisor considers a company to be a small cap company if it has a float adjusted market capitalization at the time of purchase of $5 billion or less. Securities of companies whose float adjusted market capitalization no longer meets this definition of small cap company after purchase may continue to be held in the Fund. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund's investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 35% of its net assets or twice the emerging markets component of the MSCI All Country World Ex-U.S. Small Cap Index (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.<br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/>The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.<b>PRINCIPAL RISKS OF INVESTING: </b>The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of foreign companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. These foreign investment risks are magnified in less-established, emerging markets. In addition, the Fund may invest in the securities of smaller companies, which may be more volatile and less liquid than securities of large companies. In addition, smaller companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance. The Fund is designed for long-term investors.<b>SUMMARY<br/>WILLIAM BLAIR INTERNATIONAL EQUITY FUND</b>This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of foreign companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. These foreign investment risks are magnified in less-established, emerging markets. In addition, the Fund may invest in the securities of smaller companies, which may be more volatile and less liquid than securities of large companies. In addition, smaller companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance. The Fund is designed for long-term investors.Under normal market conditions, the Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by companies of all sizes domiciled outside the U.S. that the Advisor believes have above-average growth, profitability and quality characteristics. Under normal market conditions, the Fund typically holds a limited number of securities (i.e., 40-80 securities). The Advisor seeks investment opportunities in companies at different stages of development ranging from large, well-established companies to smaller companies at earlier stages of development, that are leaders in their country, industry or globally in terms of products, services or execution. The Fund&#8217;s investments are normally allocated among at least six different countries and no more than 50% of the Fund&#8217;s equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund&#8217;s investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 40% of its net assets or twice the emerging markets component of the MSCI All Country World Ex-U.S. Investable Market Index (IMI) (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.<br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons. <br/><br/>The Advisor will vary the Fund&#8217;s sector and geographic diversification based upon the Advisor&#8217;s ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.<b>PRINCIPAL RISKS OF INVESTING:</b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 82% of the average value of its portfolio.<b>SUMMARY</b><br /><b>WILLIAM BLAIR MID CAP GROWTH FUND</b><b>FUND PERFORMANCE HISTORY:</b>The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of foreign small cap companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. These foreign investment risks are magnified in less-established, emerging markets. In addition, the Fund invests primarily in the securities of small cap companies, which may be more volatile and less liquid than securities of large companies. In addition, small cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. These risks are intensified for investments in micro-cap companies (i.e., companies with market capitalizations of $250 million or less). To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>: </b>Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of medium capitalized ("mid cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of mid cap domestic growth companies that are expected to exhibit quality growth characteristics. For purposes of the Fund, the Advisor considers a company to be a mid cap company if it has a market capitalization no smaller than the smallest capitalized company, and no larger than the largest capitalized company, included in the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to mid cap companies, but that may have a market capitalization above the market capitalization of the largest member, or below the market capitalization of the smallest member, of the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index.<br/><br/> The Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index measures the performance of the 800 companies with the lowest market capitalizations in the Russell 1000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index. The companies in the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index are considered representative of mid cap companies. The size of companies in the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index may change with market conditions. In addition, changes to the composition of the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index can change the market capitalization range of companies included in the index. As of June 22, 2012, the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index included securities issued by companies that ranged in size between $660 million and $20 billion.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor evaluates the extent to which a company meets the quality growth criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be or should have the expectation of becoming, a significant provider in the primary markets it serves, (b) the company should have some distinctive attribute relative to present or potential competitors (this may take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition), (c) the company should participate in an industry expected to grow rapidly due to economic factors or technological change or should grow through market share gains in its industry and (d) the company should have a strong management team.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly</b><br/> <b>Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">18.50% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(22.49)% (4Q08)</p></td></tr></table><b>FUND PERFORMANCE HISTORY:</b><b>Average Annual Total Returns</b> (For the periods ended December 31, 2012).<b>INVESTMENT OBJECTIVE:</b><b>Annual Total Returns.</b>0.62The Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the last ten calendar years.1-800-635-2886www.williamblair.com<b>SUMMARY<br/>WILLIAM BLAIR GLOBAL SMALL CAP GROWTH FUND</b>The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.The William Blair Global Small Cap Growth Fund seeks long-term capital appreciation.<b>FEES AND EXPENSES:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.April 30, 2014This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.<b>Average Annual Total Returns </b> (For the periods ended December 31, 2012)<b>.</b>After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.0.89After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.The Fund's returns will vary, and you could lose money by investing in the Fund.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Annual Total Returns.</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.<b>Highest Quarterly Return</b>1-800-635-28862009-06-30<b>FUND PERFORMANCE HISTORY:</b>0.185www.williamblair.com<b>Lowest Quarterly Return</b>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.2008-12-31The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.-0.2249<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b>After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Example:</b><b>Highest Quarterly Return</b><b>Annual Total Returns.</b>2009-06-30This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:0.3726The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.<b>Lowest Quarterly Return</b><b>Portfolio Turnover:</b>2008-12-31-0.2984<b>Average Annual Total Returns </b> (For the periods ended December 31, 2012)<b>.</b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. Because the Fund is newly organized, portfolio turnover information is not available.<b>PRINCIPAL INVESTMENT STRATEGIES:</b><b>Average Annual Total Returns </b> (For the periods ended December 31, 2012).00<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly</b> <b>Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">28.45% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(26.49)% (3Q08)</p></td></tr></table>-0.01The Fund&#8217;s returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of foreign companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Because the Fund may focus its investments in a limited number of securities, its performance may be more volatile than a fund that invests in a greater number of securities. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund&#8217;s investments. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. These foreign investment risks are magnified in less-established, emerging markets. In addition, the Fund may invest in the securities of smaller companies, which may be more volatile and less liquid than securities of large companies. In addition, smaller companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Because the Fund is new, investors bear the risk that the Fund may not be able to implement its investment strategies or attract sufficient assets. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.<b>FUND PERFORMANCE HISTORY:</b>The bar chart and table showing the Fund&#8217;s annual returns and average annual total return are not included because the Fund does not have annual returns for a full calendar year.Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small capitalization ("small cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by small cap companies worldwide that the Advisor believes have above average growth, profitability and quality characteristics. For purposes of the Fund, the Advisor considers a company to be a small cap company if it has a float adjusted market capitalization at the time of purchase of $5 billion or less. Securities of companies whose float adjusted market capitalization no longer meets this definition of small cap after purchase may continue to be held in the Fund. The Fund's investments are normally allocated among at least six different countries and no more than 65% of the Fund's equity holdings may be invested in securities of issuers in any one country at any given time. Under normal market conditions at least 40% of the Fund's assets will be invested in companies located outside the United States. Normally, the Fund's investments will be divided among the United States, Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 35% of its net assets or twice the emerging markets component of the MSCI All Country World (ACWI) Small Cap Index (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of emerging market companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/> The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of global small cap companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. These foreign investment risks are magnified in less-established, emerging markets. In addition, the Fund invests primarily in the securities of small cap companies, which may be more volatile and less liquid than securities of large companies. In addition, small cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. These risks are intensified for investments in micro-cap companies (i.e., companies with market capitalizations of $250 million or less). To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Because the Fund is new, investors bear the risk that the Fund may not be able to implement its investment strategies or attract sufficient assets. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly</b><br/> <b>Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">32.80% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(29.31)% (4Q08)</p></td></tr></table><b>PRINCIPAL RISKS OF INVESTING:</b>-0.01<b>FUND PERFORMANCE HISTORY:</b>0.0095The bar chart and table showing the Fund&#8217;s annual returns and average annual total return are not included because the Fund does not have annual returns for a full calendar year.The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.00.810.0012<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly</b><br/> <b>Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">23.02% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(27.09)% (3Q08)</p></td></tr></table>0.011The Fund's returns will vary, and you could lose money by investing in the Fund.00.01070.00250.01350.01250.76The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.01-800-635-2886www.williamblair.com0-0.02-0.001-0.02The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future109The Fund's returns will vary, and you could lose money by investing in the Fund.3405900.0113060.00410.0141The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.0.00950.01401-800-635-2886www.williamblair.com0.0057After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.0.0152After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.0.012After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.127-0.0032After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.-0.000100.6215<b>Highest Quarterly Return</b>0.2754-0.29310.01481430.1442-0.01882009-06-300.2845445<b>Lowest Quarterly Return</b>2008-12-31-0.4672008-09-30<b>Lowest Quarterly Return</b>0.7002-0.26490.16620.3282009-06-30-0.1313122<b>Highest Quarterly Return</b>0.1843<b>FUND PERFORMANCE HISTORY:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Total Returns.</b>The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.0.1600-0.020.1130.10920.07850.15810.04710.04380.04030.03230.06220.05810.05330.0457-0.02The Fund's returns will vary, and you could lose money by investing in the Fund.April 30, 20140.010The Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.&#8220;Other Expenses&#8221; are estimated for the current fiscal year since the Fund did not commence operations until April 10, 2013.1-800-635-28860.003www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.0.013After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the "Return After Taxes on Distributions and Sale of Fund Shares" may be greater than the "Return Before Taxes" because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.0.1495132-0.3450.18430.18350.12070.14590.01690.01480.01330.03490.36360.24310.09860.09120.08540.0980.01860.113<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairInternationalLeadersFundClassI column period compact * ~</div>
The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairInternationalLeadersFundClassI column period compact * ~</div>
The bar chart and table showing the Fund&#8217;s annual returns and average annual total return are not included because the Fund does not have annual returns for a full calendar year.0.211April 30, 2014-0.11840.23770.80.7418The Fund's returns will vary, and you could lose money by investing in the Fund.-0.616The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.0.38130.38071-800-635-2886www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">4.86% (3Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(1.63)% (3Q08)</p></td></tr></table>In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Highest Quarterly Return</b>2009-06-3000.2302<b>Lowest Quarterly Return</b>2008-09-30-0.27090.0100.0020.0120.011This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.0.2110.2060.14120.1852<b>INVESTMENT OBJECTIVE:</b>0.00560.00360.0042-0.0039<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairSmallCapGrowthFundClassI column period compact * ~</div>
0.06490.06120.05570.0599<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualFundOperatingExpensesWilliamBlairSmallCapGrowthFundClassI column period compact * ~</div>
<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairSmallCapGrowthFundClassI column period compact * ~</div>
0.0100.0015<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairSmallCapGrowthFundClassIBarChart column period compact * ~</div>
0.0115<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairMidCapGrowthFundClassIBarChart column period compact * ~</div>
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0-0.020.0111170.0034Thus, the Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairMidCapGrowthFundClassI column period compact * ~</div>
www.williamblair.com112The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualFundOperatingExpensesWilliamBlairMidCapGrowthFundClassI column period compact * ~</div>
0.0144After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairMidCapGrowthFundClassI column period compact * ~</div>
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In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.-0.0024You may obtain the most current yield information for the Fund1-800-742-7272<b>Highest Quarterly Return</b>2009-09-300.0486<b>Lowest Quarterly Return</b>2008-09-30-0.01630.0120.250.13580.11050.42420.09950.18790.12542005-11-012005-11-012005-11-012005-11-010.22-0.37540.23350.44260.18530.2305<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>0.0001-0.5217The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.0.12360.4263<b>Yield:</b> You may obtain the most current yield information for the Fund by calling 1-800-742-7272.0.2047-0.14230.2396April 30, 2014<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairBondFund column period compact * ~</div>
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0.17890.17110.12160.1641-0.048-0.0503-0.0407-0.03430.04280.03950.0370.0598<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualFundOperatingExpensesWilliamBlairInternationalLeadersFundClassI column period compact * ~</div>
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This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairInternationalEquityFundClassI column period compact * ~</div>
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0.12360.11890.08660.16130.0450.04070.03790.04070.0760.07030.06550.0707<b>SUMMARY</b><br/><b>WILLIAM BLAIR SMALL-MID CAP GROWTH FUND</b><b>Shareholder Fees</b> (fees paid directly from your investment)<b>: </b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>: </b>The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of small cap and mid cap domestic growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. The securities of small cap and mid cap companies may be more volatile and less liquid than securities of large cap companies. In addition, small and mid cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.<b>PRINCIPAL RISKS OF INVESTING: </b><b>PRINCIPAL INVESTMENT STRATEGIES: </b><table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">22.28% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(23.28)% (4Q08)</p></td></tr></table><b>Average Annual Total Returns</b> (For the periods ended December 31, 2012).Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of small capitalized ("small cap") and medium capitalized ("mid cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of small cap and mid cap domestic growth companies that are expected to exhibit quality growth characteristics. For purposes of the Fund, the Advisor considers a company to be a small cap or mid cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index at the time of the Fund's investment. Securities of companies whose market capitalization no longer meets this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to small cap and mid cap companies, but that may have a market capitalization above the market capitalization of the largest member of the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index.<br/><br/> The Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index measures the performance of the 800 companies with the lowest market capitalizations in the Russell 1000<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index. The size of companies in the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index may change with market conditions. In addition, changes to the composition of the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index can change the market capitalization range of companies included in the index. As of June 22, 2012, the Russell Midcap<sup style="POSITION: relative; BOTTOM: 0.8ex; VERTICAL-ALIGN: baseline">&#174;</sup> Index included securities issued by companies that ranged in size between $660 million and $20 billion.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor evaluates the extent to which a company meets the quality growth criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be or should have the expectation of becoming, a significant provider in the primary markets it serves, (b) the company should have some distinctive attribute relative to present or potential competitors (this may take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition), (c) the company should participate in an industry expected to grow rapidly due to economic factors or technological change or should grow through market share gains in its industry and (d) the company should have a strong management team.2003-12-292003-12-292003-12-290.82April 30, 2014The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.<b>Highest Quarterly Return</b>2009-06-300.2228<b>Lowest Quarterly Return</b>2008-12-31-0.2328After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.-0.001-0.012006-02-012006-02-012006-02-012006-02-01<b>SUMMARY</b><br/><b>WILLIAM BLAIR INCOME FUND</b><b>INVESTMENT OBJECTIVE:</b>The William Blair Income Fund seeks a high level of current income with relative stability of principal.This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.<b>Shareholder Fees</b> (fees paid directly from your investment):<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment):April 30, 20140.56The Fund's returns will vary, and you could lose money by investing in the Fund.This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886www.williamblair.com&#8220;Other Expenses&#8221; are estimated for the current fiscal year since the Fund did not commence operations until August 16, 2012.The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 33% of the average value of its portfolio.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Highest&nbsp;Quarterly Return</b>2012-03-310.0967<b>PRINCIPAL INVESTMENT STRATEGIES: </b><b>Lowest&nbsp;Quarterly Return</b>2012-06-30-0.0462<b>FUND PERFORMANCE HISTORY:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Total Returns.</b>The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the last ten calendar years.<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012).The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>Yield:</b> You may obtain the most current yield information for the Fund by calling 1-800-742-7272.The Fund is subject to credit risk. The Fund's net asset value and total return may be adversely affected by the inability of the issuers of the Fund's securities to make interest payments or payment at maturity. The Fund's investments in obligations issued or guaranteed by U.S. Government agencies or instrumentalities may not be backed by the full faith and credit of the United States and may differ in the degree of support provided by the U.S. Government. The Fund is also subject to interest rate risk. The value of income producing securities will generally decrease when interest rates rise, which means the Fund's net asset value and total returns will likewise decrease in a rising interest rate environment. As of the date of this Prospectus, interest rates continue to be at historic lows. Investments with longer maturities, which typically provide higher yields than securities with shorter maturities, may subject the Fund to increased price changes resulting from market yield fluctuations. The Fund's investments in collateralized mortgage obligations are subject to prepayment and extension risk. Prepayment of high interest rate mortgage-backed securities during times of declining interest rates will tend to lower the return of the Fund and may even result in losses to the Fund if the prepaid securities were acquired at a premium. Slower prepayments during periods of rising interest rates may increase the duration of the Fund's mortgage-backed securities and asset-backed securities and reduce their value. Rule 144A securities are not registered for resale in the general securities market and may be classified as illiquid. It may not be possible to sell or otherwise dispose of illiquid securities both at the price and within a time period deemed desirable by the Fund. The Fund is also subject to income risk, which is the risk that the income received by the Fund may decrease as a result of a decline in interest rates. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Thus, the Fund's returns will vary, and you could lose money by investing in the Fund. Of course, for all mutual funds there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance.<b>PRINCIPAL RISKS OF INVESTING: </b><table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">4.59% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(3.90)% (3Q08)</p></td></tr></table>As a matter of fundamental policy, under normal market conditions, the Fund invests at least 90% of its total assets in the following: (a) U.S. dollar-denominated corporate debt securities (domestic or foreign) with long-term ratings of "A &#8211;" or better, or an equivalent rating, by at least one of the following three nationally recognized statistical rating organizations: Fitch Ratings, Moody's Investors Service, Inc. and Standard &amp; Poor's, a division of The McGraw-Hill Companies, Inc. ("Rating Organizations"); (b) obligations of or guaranteed by the U.S. Government, its agencies or instrumentalities; (c) collateralized obligations, which are debt securities issued by a corporation, trust or custodian, or by a U.S. Government agency or instrumentality, that are collateralized (i.e., secured as to payment of interest and/or principal) by a portfolio or pool of assets, such as mortgages, mortgage-backed securities, debit balances on credit card accounts or U.S. Government securities (the Fund may invest in collateralized obligations that are not guaranteed by a U.S. Government agency or instrumentality only if the collateralized obligations are rated "A &#8211;" or better, or an equivalent rating, by one of the Rating Organizations); and (d) commercial paper obligations rated within the highest grade by one of the Rating Organizations. The Fund may also invest in Rule 144A securities.<br/><br/>The Advisor seeks to outperform the Barclays U.S. Intermediate Government/Credit Bond Index through an actively managed diversified portfolio of debt securities. The Advisor's investment philosophy emphasizes shifts in the Fund's portfolio among various sectors of the debt market, subject to the Fund's credit quality constraints for its portfolio. The Advisor also actively manages the Fund based upon the average duration and yield to maturity of the Fund's portfolio and the Advisor's perceived trends in interest rates.<br/><br/>The anticipated dollar-weighted average maturity of the Fund is three to seven years. The anticipated weighted average modified duration for the Fund is two to five years, with a maximum duration on any instrument of nine years. The Advisor will not continue to hold a security whose duration has moved above nine years. The duration of an instrument is different from the maturity of an instrument in that duration measures the average period remaining until the discounted value of the amounts due (principal and interest) under the instrument are to be paid, rather than the instrument's stated final maturity. In addition, a portfolio duration of five years means that if interest rates increased by one percent, the value of the portfolio would decrease by approximately five percent. Modified duration adjusts duration to take into account the yield to maturity and the number of coupons received each year. For purposes of calculating duration, instruments allowing prepayment will be assigned a prepayment schedule by the Advisor based upon industry experience.<br/><br/>Up to 10% of the Fund's total assets may be invested in securities that at the time of purchase are debt securities that are rated lower than "A &#8211;" but at least "BBB &#8211;" (or its equivalent) by at least one of the Rating Organizations by which such securities are rated, so long as the Fund does not invest more than 3% of its total net assets in securities of any single issuer whose securities are rated "BBB &#8211;". Securities that are downgraded below "BBB &#8211;" (or its equivalent) after purchase may continue to be held in the Fund. Although considered to be investment grade, debt securities rated "BBB" may have speculative characteristics, and changes in economic conditions or other circumstances are more likely to lead to a weakened capacity to make principal and interest payments than is the case for higher grade bonds. Debt securities rated below "BBB &#8211;" (or its equivalent) are commonly referred to as "high-yield" or "junk" bonds and are considered speculative with respect to the issuer's capacity to pay interest and repay principal and are susceptible to default or decline in market value due to adverse economic and business developments. The market values for high-yield securities tend to be very volatile, and these securities are often less liquid than investment grade debt securities.2011-10-24This table describes the fees and expenses that you may pay if you buy and hold Class N shares of the Fund.0.33Thus, the Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Highest Quarterly Return</b>2009-06-300.0459<b>Lowest Quarterly Return</b>2008-09-30-0.039<b>Portfolio Turnover: </b><b>PRINCIPAL INVESTMENT STRATEGIES: </b>This example is intended to help you compare the cost of investing in Class N shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the last ten calendar years.2003-12-29You may obtain the most current yield information for the Fund1-800-742-7272The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>FEES AND EXPENSES:</b>The Fund's returns will vary, and you could lose money by investing in the Fund.The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>SUMMARY <br/>WILLIAM BLAIR BOND FUND</b><b>INVESTMENT OBJECTIVE:</b>The William Blair Bond Fund seeks to outperform the Barclays Capital U.S. Aggregate Index by maximizing total return through a combination of income and capital appreciation.<b>FEES AND EXPENSES:</b>This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.<b>Shareholder Fees</b> (fees paid directly from your investment)<b>: </b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>: </b><b>Example: </b><b>INVESTMENT OBJECTIVE:</b>This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:The William Blair Emerging Markets Growth Fund seeks long-term capital appreciation.<b>Portfolio Turnover: </b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 25% of the average value of its portfolio.<b>FEES AND EXPENSES:</b><b>PRINCIPAL INVESTMENT STRATEGIES: </b>This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.<b>Example: </b>This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>Portfolio Turnover: </b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 90% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES: </b><b>PRINCIPAL RISKS OF INVESTING: </b><b>FUND PERFORMANCE HISTORY:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Total Returns.</b>The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in bonds. Other types of income producing securities, such as convertible bonds, hybrid bonds and preferred stock, may also be considered in seeking to achieve the Fund's investment objective. The Fund's investments may have variable rates of interest. The Fund invests primarily in U.S. dollar denominated, investment grade fixed income securities. A security is considered to be investment grade if it is rated in one of the highest four categories by at least one of the following three nationally recognized statistical rating organizations: Fitch Ratings, Moody's Investors Service, Inc. and Standard &amp; Poor's, a division of The McGraw-Hill Companies, Inc. (the &#8220;Rating Organizations&#8221;). No more than 10% of the Fund's net assets may be invested in below investment grade securities (e.g., high yield or junk bonds), which are securities rated below Baa/BBB, provided that the securities are rated &#8220;B &#8211;&#8221; or better by each of the Rating Organizations issuing a rating, or, if unrated, that the Advisor deems such securities to be of at least &#8220;B &#8211;&#8221; quality at the time of purchase. The Fund's investments in below investment grade securities may have additional credit risk. In some cases, below investment grade securities may decline in credit quality or go into default.<br/><br/> The Fund's assets will principally be invested in obligations of, or guaranteed by, the U.S. Government, its agencies or instrumentalities; corporate debt securities issued by domestic and foreign companies; and mortgage-backed securities and asset-backed securities, which are debt securities issued by a corporation, trust or custodian, or by a U.S. Government agency or instrumentality, that are collateralized (i.e., secured as to payment of interest and/or principal) by a portfolio or pool of assets, such as mortgages, debit balances on credit card accounts or U.S. Government securities. The Fund may also invest in Rule 144A securities.<br/><br/> The anticipated average duration for the Fund is a range within one year longer or shorter than the average duration of the Barclays U.S. Aggregate Index (the "Benchmark"). As of March 31, 2013, the modified adjusted duration of the Benchmark was 5.26 years. The duration of an instrument is different from the maturity of an instrument in that duration measures the average period remaining until the discounted value of the amounts due (principal and interest) under the instrument are to be paid, rather than the instrument's stated final maturity. In addition, portfolio duration of five years means that if interest rates increased by one percent, the value of the portfolio would decrease by approximately five percent. For purposes of calculating duration, instruments allowing prepayment will be assigned a prepayment schedule by the Advisor based upon industry experience.<br/><br/> The Advisor emphasizes individual security selection, as well as shifts in the Fund's portfolio among market sectors. To a lesser extent, the Advisor actively manages the Fund's average duration relative to the Benchmark. The Fund does not invest in common stocks, foreign currency denominated securities or securities of which the coupon or principal payments are determined by commodity or equity indices.<b>PRINCIPAL RISKS OF INVESTING: </b>The Fund is subject to credit risk. The Fund's net asset value and total return may be adversely affected by the inability of the issuers of the Fund's securities to make interest payments or payment at maturity. The Fund's investments in obligations issued or guaranteed by U.S. Government agencies or instrumentalities may not be backed by the full faith and credit of the United States and may differ in the degree of support provided by the U.S. Government. The Fund is also subject to interest rate risk. The value of income producing securities will generally decrease when interest rates rise, which means the Fund's net asset value and total returns will likewise decrease in a rising interest rate environment. As of the date of this Prospectus, interest rates continue to be at historic lows. Investments with longer maturities, which typically provide higher yields than securities with shorter maturities, may subject the Fund to increased price changes resulting from market yield fluctuations. The Fund's investments in mortgage-backed securities and asset-backed securities are subject to prepayment and extension risk. Prepayment of high interest rate mortgage-backed securities and asset-backed securities during times of declining interest rates will tend to lower the return of the Fund and may even result in losses to the Fund if the prepaid securities were acquired at a premium. Slower prepayments during periods of rising interest rates may increase the duration of the Fund's mortgage-backed securities and asset-backed securities and reduce their value. Rule 144A securities are not registered for resale in the general securities market and may be classified as illiquid. The Fund's investments in below investment grade securities may be less liquid than investment grade securities. It may not be possible to sell or otherwise dispose of illiquid securities both at the price and within a time period deemed desirable by the Fund.<br/><br/> The Fund is also subject to income risk, which is the risk that the income received by the Fund may decrease as a result of a decline in interest rates. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Thus, the Fund's returns will vary, and you could lose money by investing in the Fund. Of course, for all mutual funds there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance.<b>FUND PERFORMANCE HISTORY:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Total Returns.</b>The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.<b>INVESTMENT OBJECTIVE:</b>The William Blair Institutional International Equity Fund seeks long-term capital appreciation.<b>FEES AND EXPENSES:</b>This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>Example: </b><b>PRINCIPAL INVESTMENT STRATEGIES: </b><table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">4.91% (3Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(1.60)% (3Q08)</p></td></tr></table><b>PRINCIPAL RISKS OF INVESTING: </b><b>SUMMARY </b><br/><b>WILLIAM BLAIR EMERGING MARKETS SMALL CAP GROWTH FUND</b><b>INVESTMENT OBJECTIVE:</b><b>Annual Total Returns.</b>The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.<b> SUMMARY<br/>WILLIAM BLAIR INSTITUTIONAL INTERNATIONAL EQUITY FUND </b><b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>This example is intended to help you compare the cost of investing in shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 86% of the average value of its portfolio.Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by foreign large capitalization ("large cap") and medium capitalization ("mid cap") companies that the Advisor believes have above-average growth, profitability and quality characteristics. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund's investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest up to 30% of its net assets in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries. To a limited extent, the Fund may also invest in small capitalization ("small cap") companies.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/> The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of foreign companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. These foreign investment risks are magnified in less-established, emerging markets. In addition, the Fund may invest in the securities of smaller companies, which may be more volatile and less liquid than securities of large companies. In addition, smaller companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/> <b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance. The Fund is designed for long-term investors.<b>FUND PERFORMANCE HISTORY:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.April 30, 2014000.250.0100.00160.01160.011Thus, the Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886www.williamblair.com112363633The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.1404After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.0.1826After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.0.2022In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.0.1836-0.49570.33270.1112The William Blair Emerging Markets Small Cap Growth Fund seeks long-term capital appreciation.-0.12120.1831<b>Yield:</b> You may obtain the most current yield information for the Fund by calling 1-800-742-7272.<b>SUMMARY<br/>WILLIAM BLAIR EMERGING MARKETS GROWTH FUND </b>0.18310.18070.12220.1641<b>Shareholder Fees</b> (fees paid directly from your investment)<b>: </b><b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>: </b>-0.0493-0.0516-0.0417-0.0343Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in emerging markets securities. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by emerging market companies of all sizes that the Advisor believes have above-average growth, profitability and quality characteristics. Emerging market companies, for purposes of the Fund, are companies organized under the laws of an emerging market country or that have securities traded principally on an exchange or over-the-counter in an emerging market country. Currently, emerging markets include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of emerging market companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/> The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of emerging market companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. These risks may be greatly increased in emerging market countries because the securities of emerging market companies may be subject to greater volatility and less liquidity than companies in more developed markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The currencies of emerging market countries may experience a devaluation relative to the U.S. dollar, and continued devaluations may adversely affect the value of the Fund's assets denominated in such currencies. Many emerging market countries have experienced substantial rates of inflation for many years, and continued inflation may adversely affect the economies and securities markets of such countries. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. In addition, the Fund may invest in the securities of smaller companies, which may be more volatile and less liquid than securities of large companies. In addition, smaller companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.0.03620.03150.03070.0432<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">34.05% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(32.67)% (3Q08)</p></td></tr></table><b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>You may obtain the most current yield information for the Fund1-800-742-7272<b>Highest Quarterly Return </b>2009-09-300.0491<b>Lowest Quarterly Return</b>2008-09-30-0.016<b>FEES AND EXPENSES:</b>This table describes the fees and expenses that you may pay if you buy and hold Institutional Class shares of the Fund.<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b>00<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b><b>Example:</b>This example is intended to help you compare the cost of investing in Institutional Class shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>Portfolio Turnover:</b>0.00300.00260.0056The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 78% of the average value of its portfolio.0.90.005The Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.<b>PRINCIPAL INVESTMENT STRATEGIES:</b>1-800-635-2886www.williamblair.com-0.0006After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Highest Quarterly Return</b>2009-06-300.34050<b>Lowest Quarterly Return</b>Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of emerging market small capitalization ("small cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by emerging market small cap companies that the Advisor believes have above average growth, profitability and quality characteristics. For purposes of the Fund, the Advisor considers a company to be a small cap company if it has a float adjusted market capitalization at the time of purchase no larger than the greater of $3 billion or the largest capitalized company included in the MSCI Emerging Markets Small Cap Index (Net). Securities of companies whose float adjusted market capitalization no longer meets this definition of small cap after purchase may continue to be held in the Fund. Emerging market companies, for purposes of the Fund, are companies organized under the laws of an emerging market country or that have securities traded principally on an exchange or over-the-counter in an emerging market country. Currently, emerging markets include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of emerging market companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/>The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.2008-09-300-0.3267<b>PRINCIPAL RISKS OF INVESTING:</b>The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of emerging market small cap companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. These risks may be greatly increased in emerging market countries because the securities of emerging market companies may be subject to greater volatility and less liquidity than companies in more developed markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The currencies of emerging market countries may experience a devaluation relative to the U.S. dollar, and continued devaluations may adversely affect the value of the Fund's assets denominated in such currencies. Many emerging market countries have experienced substantial rates of inflation for many years, and continued inflation may adversely affect the economies and securities markets of such countries. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. In addition, the Fund invests primarily in the securities of small cap companies, which may be more volatile and less liquid than securities of large companies. In addition, small cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. These risks are intensified for investments in micro-cap companies (i.e., companies with market capitalizations of $250 million or less). To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Because the Fund is new, investors bear the risk that the Fund may not be able to implement its investment strategies or attract sufficient assets. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.The Fund's returns will vary, and you could lose money by investing in the Fund.The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.1-800-635-2886www.williamblair.comThe Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.0.0095After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.0In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.0.0042511730.0137-0.003200.0105<b>FUND PERFORMANCE HISTORY<sup>(1)</sup>:</b>307696<b>Highest Quarterly Return</b>2009-06-300.2309<b>Lowest Quarterly Return</b>2008-09-30-0.27471074020.01727190.11416180.07890.07620.08540.08540.06870.05660.04210.07390.0560.0530.05950.07140.05370.05090.0611-0.02<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairInternationalLeadersFundInstitutionalClass column period compact * ~</div>
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0.01412007-05-012007-05-012007-05-012007-05-01<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairInternationalLeadersFundInstitutionalClass column period compact * ~</div>
<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">23.09% (2Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(27.47)% (3Q08)</p></td></tr></table>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<br /><br />2004-12-012004-12-012004-12-012004-12-011444467711691<b>Annual Total Returns.</b>The bar chart below provides an illustration of the Fund&#8217;s performance in the calendar year since the Fund started.April 30, 20140.160.21010.20860.13850.1868The Fund's returns will vary, and you could lose money by investing in the Fund.-0.0363-0.0457-0.0336-0.007The bar chart and table showing the Fund&#8217;s annual returns and average annual total return are not included because the Fund does not have annual returns for a full calendar year.0.11390.10050.0970.115<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly</b> <b>Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">21.07% (1Q12)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(5.43)% (2Q12)</p></td></tr></table>-0.0006<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012).The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b> SUMMARY<br/>WILLIAM BLAIR INTERNATIONAL LEADERS FUND</b><b>INVESTMENT OBJECTIVE: </b>The William Blair International Leaders Fund seeks long-term capital appreciation.<b>FEES AND EXPENSES: </b>This table describes the fees and expenses that you may pay if you buy and hold Institutional Class shares of the Fund.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairBondFundClassI column period compact * ~</div>
<b>Shareholder Fees</b> (fees paid directly from your investment):<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment):<b>Example: </b>This example is intended to help you compare the cost of investing in Institutional Class shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualFundOperatingExpensesWilliamBlairBondFundClassI column period compact * ~</div>
<b>Portfolio Turnover: </b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal period (August 16, 2012 through December 31, 2012), the Fund&#8217;s portfolio turnover rate was 16% of the average value of its portfolio.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleExpenseExampleTransposedWilliamBlairBondFundClassI column period compact * ~</div>
<b>PRINCIPAL INVESTMENT STRATEGIES:</b>Under normal market conditions, the Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by companies of all sizes domiciled outside the U.S. that the Advisor believes have above-average growth, profitability and quality characteristics. Under normal market conditions, the Fund typically holds a limited number of securities (i.e., 40-80 securities). The Advisor seeks investment opportunities in companies at different stages of development ranging from large well-established companies to smaller companies at earlier stages of development, that are leaders in their country, industry or globally in terms of products, services or execution. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund's investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 40% of its net assets or twice the emerging markets component of the MSCI All Country World Ex-U.S. Investable Market Index (IMI) (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.<br/><br/> In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/> The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.<b>PRINCIPAL RISKS OF INVESTING:</b><div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairBondFundClassIBarChart column period compact * ~</div>
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<b>SUMMARY</b><br/><b>WILLIAM BLAIR READY RESERVES FUND</b><b>INVESTMENT OBJECTIVE</b><b>:</b>0.3807<b>FEES AND EXPENSES</b><b>:</b>0.3813-0.6160.7418<b>Shareholder Fees</b> (fees paid directly from your investment)0.2377-0.17<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)0.2101<b>FUND PERFORMANCE HISTORY<sup>(1)</sup>:</b><b>PRINCIPAL INVESTMENT STRATEGIES: </b>The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of foreign companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Because the Fund may focus its investments in a limited number of securities, its performance may be more volatile than a fund that invests in a greater number of securities. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. These foreign investment risks are magnified in less-established, emerging markets. In addition, the Fund may invest in the securities of smaller companies, which may be more volatile and less liquid than securities of large companies. In addition, smaller companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone.</b> You should only consider it for the aggressive portion of your portfolio. Because the Fund is new, investors bear the risk that the Fund may not be able to implement its investment strategies or attract sufficient assets. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.<b>FUND PERFORMANCE HISTORY:</b>The bar chart and table showing the Fund&#8217;s annual returns and average annual total return are not included because the Fund does not have annual returns for a full calendar year.Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund. As with any money market fund, there is a risk that the issuers or guarantors of securities will default on the payment of principal or interest or the obligation to repurchase securities from the Fund. An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You should not rely on or expect the Advisor to purchase distressed assets, make capital infusions, enter into support agreements or take other actions to maintain the Fund&#8217;s $1.00 share price. The credit quality of the Fund&#8217;s holdings can change rapidly in certain markets, and the default of a single holding could have an adverse impact on the Fund&#8217;s share price. To the extent the Fund invests in short-term U.S. dollar-denominated foreign money market instruments, investing in foreign securities may involve a greater degree of risk than investing in domestic securities due to the possibility of, but not limited to, less publicly available information, more volatile markets, less securities regulation, less favorable tax provisions, war and expropriation. The Fund&#8217;s share price can also be negatively affected during periods of high redemption pressures and/or illiquid markets. The actions of a few large investors in the Fund may have a significant adverse effect on the share price of the Fund. Because the Fund may concentrate its assets in the banking industry, the Fund&#8217;s performance may depend in large part on that industry. Of course, for all mutual funds there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result.2005-06-062005-06-062005-06-062005-06-06000.01100.01220.02320.0125-0.0107127622114325730.34620.34450.22720.22220.25490.25360.21730.1205<b>Average Annual Total Returns (For the periods ended December 31, 2012).</b><b>Annual Total Returns.</b>2011-10-242011-10-242011-10-242011-10-24<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairEmergingMarketsGrowthFundClassI column period compact * ~</div>
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You may obtain the most current yield information for the Fund<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairEmergingMarketsGrowthFundClassIBarChart column period compact * ~</div>
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1-800-742-72720.3462The Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future.0.78The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual return for the years indicated compares with those of a broad measure of market performance.The Fund's returns will vary, and you could lose money by investing in the Fund.<b>SUMMARY<br/> WILLIAM BLAIR BOND FUND</b><b>INVESTMENT OBJECTIVE:</b>The William Blair Bond Fund seeks to outperform the Barclays Capital U.S. Aggregate Index by maximizing total return through a combination of income and capital appreciation.<b>FEES AND EXPENSES:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance.This table describes the fees and expenses that you may pay if you buy and hold Institutional Class shares of the Fund.www.williamblair.com<b>Shareholder Fees</b> (fees paid directly from your investment)<b>: </b>1-800-635-2886<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>: </b>The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.<b>Example: </b>This example is intended to help you compare the cost of investing in Institutional Class shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>Portfolio Turnover:</b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 25% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES:</b>After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.0After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.2009-12-31<b>Lowest Quarterly Return</b>0.01312001-03-31<b>Highest Quarterly Return</b>In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.<b>Highest Quarterly Return</b>2012-03-310.2107<b>Lowest Quarterly Return</b>00-0.05430.0024<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleShareholderFeesWilliamBlairEmergingMarketsSmallCapGrowthFundInstitutionalClass column period compact * ~</div>
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<b>INVESTMENT OBJECTIVE:</b>The William Blair Emerging Markets Small Cap Growth Fund seeks long-term capital appreciation.0.86<b>FEES AND EXPENSES:</b>This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.<div style="display:none">~ http://www.williamblairfunds.com/role/ScheduleAnnualTotalReturnsWilliamBlairEmergingMarketsSmallCapGrowthFundInstitutionalClassBarChart column period compact * ~</div>
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The William Blair Low Duration Fund seeks to maximize total return. Total return includes both income and capital appreciation.Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in bonds. Other types of income producing securities, such as convertible bonds, hybrid bonds and preferred stock, may also be considered in seeking to achieve the Fund's investment objective. The Fund's investments may have variable rates of interest. The Fund invests primarily in U.S. dollar denominated, investment grade fixed income securities. A security is considered to be investment grade if it is rated in one of the highest four categories by at least one of the following three nationally recognized statistical rating organizations: Fitch Ratings, Moody's Investors Service, Inc. and Standard &amp; Poor's, a division of The McGraw-Hill Companies, Inc. (the &#8220;Rating Organizations&#8221;). No more than 10% of the Fund's net assets may be invested in below investment grade securities (e.g., high yield or junk bonds), which are securities rated below Baa/BBB, provided that the securities are rated &#8220;B &#8211;&#8221; or better by each of the Rating Organizations issuing a rating, or, if unrated, that the Advisor deems such securities to be of at least &#8220;B &#8211;&#8221; quality at the time of purchase. The Fund's investments in below investment grade securities may have additional credit risk. In some cases, below investment grade securities may decline in credit quality or go into default.<br/><br/> The Fund's assets will principally be invested in obligations of, or guaranteed by, the U.S. Government, its agencies or instrumentalities; corporate debt securities issued by domestic and foreign companies; and mortgage-backed securities and asset-backed securities, which are debt securities issued by a corporation, trust or custodian, or by a U.S. Government agency or instrumentality, that are collateralized (i.e., secured as to payment of interest and/or principal) by a portfolio or pool of assets, such as mortgages, debit balances on credit card accounts or U.S. Government securities. The Fund may also invest in Rule 144A securities.<br/><br/> The anticipated average duration for the Fund is a range within one year longer or shorter than the average duration of the Barclays U.S. Aggregate Index (the "Benchmark"). As of March 31, 2013, the modified adjusted duration of the Benchmark was 5.26 years. The duration of an instrument is different from the maturity of an instrument in that duration measures the average period remaining until the discounted value of the amounts due (principal and interest) under the instrument are to be paid, rather than the instrument's stated final maturity. In addition, portfolio duration of five years means that if interest rates increased by one percent, the value of the portfolio would decrease by approximately five percent. For purposes of calculating duration, instruments allowing prepayment will be assigned a prepayment schedule by the Advisor based upon industry experience.<br/><br/> The Advisor emphasizes individual security selection, as well as shifts in the Fund's portfolio among market sectors. To a lesser extent, the Advisor actively manages the Fund's average duration relative to the Benchmark. The Fund does not invest in common stocks, foreign currency denominated securities or securities of which the coupon or principal payments are determined by commodity or equity indices.<b>PRINCIPAL RISKS OF INVESTING:</b>The Fund is subject to credit risk. The Fund's net asset value and total return may be adversely affected by the inability of the issuers of the Fund's securities to make interest payments or payment at maturity. The Fund's investments in obligations issued or guaranteed by U.S. Government agencies or instrumentalities may not be backed by the full faith and credit of the United States and may differ in the degree of support provided by the U.S. Government. The Fund is also subject to interest rate risk. The value of income producing securities will generally decrease when interest rates rise, which means the Fund's net asset value and total returns will likewise decrease in a rising interest rate environment. As of the date of this Prospectus, interest rates continue to be at historic lows. Investments with longer maturities, which typically provide higher yields than securities with shorter maturities, may subject the Fund to increased price changes resulting from market yield fluctuations. The Fund's investments in mortgage-backed securities and asset-backed securities are subject to prepayment and extension risk. Prepayment of high interest rate mortgage-backed securities and asset-backed securities during times of declining interest rates will tend to lower the return of the Fund and may even result in losses to the Fund if the prepaid securities were acquired at a premium. Slower prepayments during periods of rising interest rates may increase the duration of the Fund's mortgage-backed securities and asset-backed securities and reduce their value. Rule 144A securities are not registered for resale in the general securities market and may be classified as illiquid. The Fund's investments in below investment grade securities may be less liquid than investment grade securities. It may not be possible to sell or otherwise dispose of illiquid securities both at the price and within a time period deemed desirable by the Fund. The Fund is also subject to income risk, which is the risk that the income received by the Fund may decrease as a result of a decline in interest rates. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. Thus, the Fund's returns will vary, and you could lose money by investing in the Fund. Of course, for all mutual funds there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets invested in the Fund. In such instances, the Advisor's decision to make changes to or rebalance its clients' allocations in the separate accounts may substantially impact the Fund's performance.This table describes the fees and expenses that you may pay if you buy and hold Class I shares of the Fund.<b>FUND PERFORMANCE HISTORY:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with those of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.0<b>Annual Total Returns.</b><b>Example:</b>This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:0.00010.0001<b>Portfolio Turnover:</b>0.0001The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 78% of the average value of its portfolio.The bar chart below provides an illustration of how the Fund&#8217;s performance has varied in each of the calendar years since the Fund started.<b>PRINCIPAL INVESTMENT STRATEGIES:</b>0.0010<b>PRINCIPAL RISKS OF INVESTING:</b>0.0220.0475<b>FUND PERFORMANCE HISTORY:</b>0.0447<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>0.0262<b>Annual Total Returns.</b>0.008The bar chart below provides an illustration of the Fund&#8217;s performance in the calendar year since the Fund started.0.0066The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>Yield:</b> You may obtain the most current yield information for the Fund by calling 1-800-742-7272.0.0030<b>INVESTMENT OBJECTIVE:</b>The William Blair Low Duration Fund seeks to maximize total return. Total return includes both income and capital appreciation.0.0027<b>FEES AND EXPENSES:</b>This table describes the fees and expenses that you may pay if you buy and hold Institutional Class shares of the Fund.<b>Example:</b>0.0057<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly</b><br/> <b>Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">4.86% (3Q09)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(1.57)% (3Q08)</p></td></tr></table><b>Example: </b><b>Portfolio Turnover:</b>This example is intended to help you compare the cost of investing in Institutional Class shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>PRINCIPAL RISKS OF INVESTING:</b>0.0055<b>Portfolio Turnover:</b>The Fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund&#8217;s performance. During the most recent fiscal year, the Fund&#8217;s portfolio turnover rate was 20% of the average value of its portfolio.<b>PRINCIPAL INVESTMENT STRATEGIES:</b><b>PRINCIPAL RISKS OF INVESTING:</b>-0.0002April 30, 2014<b>FUND PERFORMANCE HISTORY:</b>The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund&#8217;s performance from year to year and by showing how the Fund&#8217;s average annual returns for the years indicated compare with that of a broad measure of market performance. The Fund&#8217;s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblair.com or call 1-800-635-2886.<b>Annual Total Returns.</b>The table shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the &#8220;Return After Taxes on Distributions and Sale of Fund Shares&#8221; may be greater than the &#8220;Return Before Taxes&#8221; because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor&#8217;s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.<b>Example: </b>This example is intended to help you compare the cost of investing in Class I shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund&#8217;s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:<b>FUND PERFORMANCE HISTORY:</b>The bar chart and table showing the Fund&#8217;s annual returns and average annual total return are not included because the Fund does not have annual returns for a full calendar year.<b>SUMMARY<br/>WILLIAM BLAIR EMERGING MARKETS SMALL CAP GROWTH FUND </b>56<b>Shareholder Fees</b> (fees paid directly from your investment)<b>:</b>181<b>Annual Fund Operating Expenses</b> (expenses that you pay each year as a percentage of the value of your investment)<b>:</b>316<b>Average Annual Total Returns</b> (For the periods ended December 31, 2012)<b>.</b>127Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of emerging market small capitalization ("small cap") companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by emerging market small cap companies that the Advisor believes have above average growth, profitability and quality characteristics. For purposes of the Fund, the Advisor considers a company to be a small cap company if it has a float adjusted market capitalization at the time of purchase no larger than the greater of $3 billion or the largest capitalized company included in the MSCI Emerging Markets Small Cap Index (Net). Securities of companies whose float adjusted market capitalization no longer meets this definition of small cap after purchase may continue to be held in the Fund. Emerging market companies, for purposes of the Fund, are companies organized under the laws of an emerging market country or that have securities traded principally on an exchange or over-the-counter in an emerging market country. Currently, emerging markets include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries. The Fund's investments are normally allocated among at least six different countries and no more than 50% of the Fund's equity holdings may be invested in securities of issuers in one country at any given time.<br/><br/>In choosing investments, the Advisor performs fundamental company analysis and focuses on stock selection. The Advisor generally seeks equity securities, including common stocks, of emerging market companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.<br/><br/>The Advisor will vary the Fund's sector and geographic diversification based upon the Advisor's ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Advisor will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.399The Fund's returns will vary, and you could lose money by investing in the Fund. Because the Fund invests most of its assets in equity securities of emerging market small cap companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of those companies or market and economic conditions. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Advisor may fail to produce its intended result. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Advisor for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Foreign investments often involve additional risks, including political instability, differences in financial reporting standards and less stringent regulation of securities markets. These risks may be greatly increased in emerging market countries because the securities of emerging market companies may be subject to greater volatility and less liquidity than companies in more developed markets. Because the securities held by the Fund usually will be denominated in currencies other than the U.S. dollar, changes in foreign currency exchange rates may adversely affect the value of the Fund's investments. The currencies of emerging market countries may experience a devaluation relative to the U.S. dollar, and continued devaluations may adversely affect the value of the Fund's assets denominated in such currencies. Many emerging market countries have experienced substantial rates of inflation for many years, and continued inflation may adversely affect the economies and securities markets of such countries. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments. In addition, the Fund invests primarily in the securities of small cap companies, which may be more volatile and less liquid than securities of large companies. In addition, small cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell the security on short notice at a reasonable price. These risks are intensified for investments in micro-cap companies (i.e., companies with market capitalizations of $250 million or less). To the extent the Fund invests a significant portion of its assets in one country, the Fund will be more vulnerable to the risks of adverse economic or political forces in that country.<br/><br/><b>The Fund involves a high level of risk and may not be appropriate for everyone</b><b>.</b> You should only consider it for the aggressive portion of your portfolio. Because the Fund is new, investors bear the risk that the Fund may not be able to implement its investment strategies or attract sufficient assets. Separate accounts managed by the Advisor may invest in the Fund and, therefore, the Advisor at times may have discretionary authority over a significant portion of the assets in the Fund. In such instances, the Advisor&#8217;s decision to make changes to or rebalance its clients&#8217; allocations in the separate accounts may substantially impact the Fund&#8217;s performance. The Fund is designed for long-term investors.<table style="BORDER-COLLAPSE: collapse" border="0" cellspacing="0" cellpadding="0" width="100%" align="center"><tr><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Highest&nbsp;Quarterly Return</b></p><p style="margin-top: 0px; margin-bottom: 1px" align="center">21.07% (1Q12)</p></td><td valign="bottom">&nbsp;</td><td valign="top"><p style="border-bottom: #000000 1px solid; margin-top: 0px; margin-bottom: 0px" align="center"><b>Lowest&nbsp;Quarterly</b><br/><b> Return</b></p><p style="MARGIN-TOP: 0px; margin-bottom: 1px" align="center">(5.43)% (2Q12)</p></td></tr></table>00The Fund is subject to credit risk. The Fund's net asset value and total return may be adversely affected by the inability of the issuers of the Fund's securities to make interest payments or payment at maturity. The Fund's investments in obligations issued or guaranteed by U.S. Government agencies or instrumentalities may not be backed by the full faith and credit of the United States and may differ in the degree of support provided by the U.S. Government. The Fund is also subject to interest rate risk. The value of income producing securities will generally decrease when interest rates rise, which means the Fund's net asset value and total returns will likewise decrease in a rising interest rate environment. As of the date of this Prospectus, interest rates continue to be at historic lows. Investments with longer maturities, which typically provide higher yields than securities with shorter maturities, may subject the Fund to increased price changes resulting from market yield fluctuations. The Fund's investments in mortgage-backed securities and asset-backed securities are subject to prepayment and extension risk.